'm r ^%. ^ nOii IMAGE EVALUATION TEST TARGET (MT-3) 1.0 ■^ 1^ 12.2 ! wa IIM I»1U>.. I.I 1.4 1.6 1.25 ^ V] orn^y /a ^^ tf*3 y /A "w r vi CIHM/ICMH Microfiche Series. CIHM/ICMH Collection de microfiches. Canadian Institute for Historical Microreproductions Institut canadien de microreproductions historiques 1980 Technical Notes / Notes techniques The Institute has attempted to obtain the best original copy available for filming. Physical features of this copy which may alter any of the images in the reproduction are checked below. D D Coloured covers/ Couvertures de couleur Coloured maps/ Cartes gdographiques en couleur Pages discoloured, stained or foxed/ Pages d6color6es, tacheties ou piqudes Tight binding (may cause shadows or distortion along interior margin)/ Reliure serrd (peut causer de I'ombre ou de la distortion le long de la marge intdrieure) L'Institut a microfilm^ le meiileur exemplaire qu'll lul a 6t6 possible de se procurer. 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The following diagrams illustrate the method: Les cartes ou les planches trop grandes pour dtre reproduites en un seui clich6 sont fiimies d partir de I'angle supirieure gauche, de gauche d droite et de haut en bas, en prenant ie nombre d'images n^cessaire. Le diagram-ne suivant illustre la mithode : 1 2 3 1 2 3 4 5 6 I 1 1 I I ON SOME DYKES CONTAINING HURONITE. BY ALFRED E. BARLOW, M.A., GEOLOGICAL SURVEY OF CAJVADA, OTTAWA. .. ».J^:. ■^ 1^ I I ■M„. J V 1^ Repriiiled frnm '1111 OlTAUA N ATri(Al.l>>T, Vol. IX., No. 2. ON SOME DYKES CONTAININC; " HURONITE." By Ai.KRED E. ;'. KLOW, M. * . Geological Survey I)e|.arlmcnl, Ottawa. Canada. ( Read hefore the Geological Society of America, /Baltimore, Dec. sStli, iS()4. ) •'• The name Huron ite was long ago given by Dr. Thonison of (Jlasf^ow, to certain light-yellowish green masses or crystals which occurred porphyritically embedded in a boulder of diabase found on the shores of Drunimond Island, Lake Huron, speciniens of which had been sent to hini by the late Dr. Holmes of Montreal. 'I'homson regarded it as a new species and published a description and analysis of it in his Mineralogy of 1836. 'i'he occurrence of these crystals was first noticed by Dr. Higsby in 1S20, who writes of the rock containing them in a general way as "greenstone porphyries having a light-colored base and containing crystals of red or white felsjjar — seldom of both in the same block,"' i) This brief and general description would not have been sufficient for pur|)oses of identification except for the fact that his manuscript report which formed the basis of this paper, (2) was lately pre- sented to the library of the (leological Survey of Canada. In the appendix Dr. Bigsby notes " among the debris of the shore of Lake Huron are por- phyries of greenstone with embedded crystals of red felspar or of four or six sided prisms of cream white colour, foliate fracture, cleavage about 60°, yielding to the knife readily, translucent at the edges and of a feel slightly soapy. Their crystallization is seldom well defined, but some- times remarkably so." This clear and accurate descri|)tion serves at (1) Trans, (icol. Soc, Lonilon, \ Ol. i, p. 205. On the Geography and Geology of Lake Huron, read t'c'.'. 21, March 7 and 21, 1823. (2) Notes on the Trpography and (jeologieal structure of the north-west jiortion of Lake Huron, addresseed officially to Dr. J. Wright, Inspeetor of Hospitals in Canada an«j(pclated (^uiKec, Teii. 23, 1S21. ^Communicated by permission of the Uirector.) 26 The Ottawa Natuualist. once to identify the substance composing these porphyntic crystals with the mineral described later by Dr. 'I'homson as " Huronite," The source of these boulders was not known and the mineral never found " in situ " until 1881, when Dr. Robert Bell, (i) of Ottawa, in his examina- tion of the country to the north-east of Lake Superior, noticed the occurrence " of a dark grey crystalline diorite (in one place rendered por- phyritic by spots of light-greenish yellow felspar) on the neck of land se- parating Lake Mattawagaming from Lake Wabatongwashene." This rather brief description waB altogether inadequate to connect the mineral with the Huronite which hud previously been described by Thomson, and it was not until Dr. Harrington, of Montreal, visited the spot on professional business some year later, that the true identity of these " spots " was clearly established. In 1891, Dr. Selwyn, of Ottawa, happened to be at the same locality which is situated between Missinaibi and Loch Alch Stations on the main line of the Canadian Pacific Railway, and he states that the dykes containing the Huronite cut both Huronian and Laurentian strata. During the construction of the Canadian Pacific Railway in 1884, Drs. Gird wood and Ruttan made a collection of the principal rocks met with on the main line from Chalk River westward- This coll tion, they subse(iuently presented to McGill University. Among the specimens, was one of a dark green diabase with pheno- orysts of a mineral resembling Huronite scattered through it. This specimen had been obtained from a dyke cutting the granitoid gneisses a few miles north-west of Pogamasing Station. The microscopical examination, however, reveals the fact that the original Drummond Island boulder was not derived from either of these localities- Mr. W. (i. Miller of the School of Mines, Kingston, who acted as Dr. Bell's Assistant in 1893, mentions the occurrence of a dyke containing Huronite near the contact between the granite and slates (Huronian) at Depot Lake in the northern part of the Township of Proctor, about fifteen miles north-east of Cook's Milla. From its geopraphical position and the direction of the glacial striae, this v.ould seem to be the most likely source of the Drummond Island boulder, although this cannot be ascertained with certainty as the specimen from the locality .^ (I) Report, (Jeolopical Survey, Canada, i88o-2, part c, p. 4. On Somk Dykkh Containing; IIukoniti:. 37 * • was lost. Mr. II. CI. Skill, of Cobourg, (hilario, who assisted the writer in nSyi, discovered another dyke containing this nuncral, ah(nit one (juarter of a mile north of Murphy i.a^ke, in Tiniher Limits yo Algoma District. During the progress of his explorations in the peninsula of Labrador, Mr. A. I'. Low, of the (leological Survey of Canada, noticed the presence of Huronite in a dyke cutting Laurentian gneisses about ten miles north of Lake Kawathagami (;n the portage route between the Rupert and l^astmain rivers and also in two dykes, each about two hundred yard.s wide, breaking through rocks of Cambrian age, on the west branch f)f the Hamilton River, fifteen and twenty miles respectively, below old Fort Nascawpee, on Lake I'elitsikapow. Dr. Harrington (private communication) has noticed loose pieces of diabase containing Huronite a few miles beyond ,\myot Station. He also mentions the occurrence of a diabase dyke four inches in width, containing phenocrysts of the same mineral, a short distance east of the crossing of the Magpie River, near Otter Station, on the Canadian Pacific Railway. Prof. N. H. Winchell, of Minneapolis, Minnesota, in his visit to the Lake Huron district, in 1889, nwde note of "the occurrence at Algoma of occasional very interesting boulders (1605). (i) They contain large and small rounded whitish green felspathic spots which are distributed somewhat like porphyritic crystals but they have not the regular periphery of crystals. They are in a matrix of ordinary diabase of dark green colour and the spots make the rock noticeable, their largest size being somewhat large^" than an inch in diameter. Some of the boulders are put in the foundation of the great hotel which the Canadian Pacific Railroad (2) l)fojected at Algoma, and that is where we saw them first. Dr. Selwyn recalled the dyke cutting the Animikie on the higl dge back of Silver Islet, as the only spot where such a rock is in ])lace," Professor Winchell, who visited this place in 1879, has sent me a small chip from a specimen then collected, as well as fragments of the Algoma boulder •C (i) The number 1,605 refers to the number of the specimen in the rock series of the Geclojjical Survey of Minnesota (2) i8th Annual Report, Geological Survey, Minnesota, 1889, pp. 58 and 63. 28 THK OlTAVVA NaTUHALIST. / and a small sainpl'j fiom a dyke near (lunflinl Lake, north-west of Lake Superior. The phenocrysts of felspar in the Silver Islet specimen, according to I'rofessor .Winchell (i) are distinctly angular and not greenish, but greyish in colour. Under the microsc()i)e, these felsDar phenocrysts are seen to be a plagioclase towards the basic end of the series (very probably labradorite) which has undergone only incipient alteration, whereas, in general the Huronite shows very great decom- position. . The writer has seen numerous boulders of diabase ccjntaining this mineral in the region to the north and northeast uf Lake Huron, especially on the shores of Lake Huron from Killamey westwaril to the mouth of the Spanish River, During the summer of 1893, the writer also noticed a boulder of dark green diabase, on the west shore of Heai Island on Lake Temagami, with plagioclase phenocrysts, which bore a very marked resemblance to the more altered Huronite. As the felspar seemed so fresh and glassy in places, it was thought an optical examination accompanied by a chemical analysis would throw a great deal of light on the original character and composition of Huronite. Dr. Harrington kindly under, 'ook the analysis of this felspar, which proves it to be labradorite. Under the microscope most ol these crystals are {|uiie fresh, although certain portions are more or less clouded by the presence of decomposition products, which it is often difficult to resolve, even with the higher powers of the microscoi)e. Certain of the crystals, however, show the same alteration, only in a lesser degree, as that which charac- terizes the Huronite. It will thus be seen that the mineral is by no means so rare as some have supposed, but has, on the contrary, a wide geographical distribu- tion. The sole reason of its not being discovered, "in situ," earlier seems to have been due to the necessarily hurried and imperfect explorations first undertaken through these wild and unsettled districts. In 1885, Dr. B. J. Harrington, of McGill University, Montreal, decided to undertake an examination of the Pogamasing mineral for purposes of comparison with that contained in the original Drummond I (i) No. 601, loth Annual Report, Geological Survey, Minnesota, [>. 56. On Somk Dykks Containing llntoNiTi;. 29 i Island boulder, a sample of wliicli was contained in the Holmes collec- tion in the Peter Redpath Museum. In the course of this investigation he discovered some very ji;rave errors in Thomson's description. "The hardness for example is about $\ instead of 3} as stated by Thomson. Instead of being infusible it is distinctly fusible (F about 5) while it con- tains alkalies the presence of which is entirely ignored by Thomson. "(i) Dana, in an old edi ion (2) of his mineral'»gy mentions Huronite under I'rehnite, evidently deeming it an allied mineral. In 1889,(3) the same author mentions Huronite along with Weissite and Ileriie as a supposed altered form of lolite (Cordierite). In the same edition (4) he also says " Thomson's Huronite is an impure anorthite-like felspar related to bytownite, according to T. S. Hunt (priv. contrib.), ex- cluding the 4" 1 6 per cent of water the Si02 would be 47 per cent of the remainder." Again, in the same edition, Dana states (5) "Huronite, Thomson (Min., I., 384, 1836) considered an altered mineral near fahlunite by T. S. Hunt, occurs in spherical masses in hornblendic boulders in the vicinity of Lake Huron." In the last edifion of Dana's Mineralogy (6) the author, Mr. E. S. Dana, places the mineral under anorthite on the authority of Dr. Harrington's paper in the Transactions of the Royal Society of Canada, but Dana is wrong in referring the analysis made by Mr. N. N. Evans, to the ^luronite of the Drummond Island boulder, for in reality it belongs to the Huronite found by Dr. Girdwood near Pogamasing. Michel-Levy and Lacroi.x(7) include Huronite among the decomposition products nf lolite or Cor- dierite. The failure to assign to Huronite its rightful mineralogical posi- tion arose from the fact that it was impossible to ascertain its true nature by chemical analysis. It remained for the microscope to dis- close its composite nature and to show its relation to the more widely known " Saussurite." (1) See Trans-Royal Soc. Canada, Section III, 1886, p. 82. (2) System of Mineralogy, 3rd edition, 1850, p. 313. (3) See System of Mineralogy, 1889, p. 301. (4) See Idem, page 34.) (5) See Idem, page 485. (6) System of Mineralogy, 1892, p 340. (7) Les Mint'ravix des Roches, 188S, p. 174. € X 30 Tin, Ottawa Natijhaliht. 11 ^ Crystals ok Hirositk in Diabahk. (Cut. No. !'!Ci. (ii' iluiriiiil Siirvi'v "I'Caimilii MmkcuiiiI From % mile N. of Murphy Lake, Algoma, Ont. The name " Huronite " has usually been restricted to jellnwish green more or less rounded masses or phenocrysts, which rarely exceed two inches in diameter, embedded in a medmm textured dark greenish or greyish groundmass. Many of the smaller and not a few of the larger individuals have an irregular or jagged outline owing to mag- matic corrosionandfrequently exhibit small armsor bays which have been filled by the invading magma. Occasionally some are seen with a more or less perfect cryslallographic outline and many exhibit one or more sharp crystal faces. The mineral is light yellowish-green in colour although portions of the crystals which h.ive undergone less alteration show a very pale flesh red or pink colour as in the case of the Murphy Lake and Eastmain specimens. The crystals weather to an opaque greyish-white forming very conspicuous spots in an other- wise dark coloured rock. Under the microscope the greenish colour is seen to be due to the more or less abundant development of » » I ; X Ox Some Dykks Containino Hurovitk. SI " I / L zoisite, epidote, sericite and chlorite at the expense of the original felspar. Some of the phenocrysts show a more or less perfect cleavage which is noticeably the case in the Eastmain specimen, although in the more hightly altered samples, as those from the vicinity of Missinaibi, little or none can be seen. Occasionally, crystals show macroscopically the lamellation due to polysynlhetic twinning, as in some of those in the Murphy Lake diabase, but as a general rule these lamellie are either absent altogether or so (aint that they cannot be detected. The mineral is sublranslucc.it, varies in lustre from pearly to waxy accord- ing to degree of alteration. The hardness varies from 5^ to 6, fusibility about 5, a'.id the specific gravity, according to Mr. R. A. A. Johnston, of the Geological Survey of Canada, varies from 2725 in the Kast- main specimen to 2 935 in those from Missinaibi. The specific gravity, as would be expected, shows an increase in proportion to the the alteration. The microscopic examination in general reveals the fact that in every case the so-called " Huronite " is really a plagioclase near the basic end of the series which has undergone inore or less complete "saussuritization." In most instances the development of zoisite, epidote, sericite, chlorite, etc., at the expense of the original felspar has been so abundant as to leave only tracts of the original twinning lammellae and occasionally to destroy all evidence of this structure. Specimens may be obtained from the large number of slides examiiied, showing a complete gradation of this decomposition from the |)ure glassy plagioclase (labradorite) composing many of the phenocrysts con- tained in the diabase from Temagami Lake to the completed Saussurite or Huronite in the porphyritic individuals of the Missinaibi rock. The matrix in which those phenocrysts are embedded is in general a typical diabase of dark greenish or greyish colour which likewise shows a wide difference in degree of alteration under the microscope. The speci- mens from Rear Island, Lake Temagami, show a very typical and fresh olivine-diabase. With the exception of some of the crystals of olivine, the rock is remarkably free from decomposition, while in the finer grained portion of the rock from Missinaibi all the component minerals have undergone great alteration. The plagioclase is more or less completely " saussuritized," the augite originally present wholly con- verted to hornblende (uralite) and the ilmenite replaced by the dull ( 8t The Ottawa Naturalist. gray almost opaque variety f sphene known as leucoxene. A strange fact noticed, moreover, is that frequently the less altered phenocrysts of Hiironite occur in an exceedingly decomposed diabase as is the case in the I'oganiasing and Eastmain specimens, while the more highly altered por|)hyritic individuals of this mineral are frequently developed in a groundmass more or less: emarkable for its freshness. This is noticeably the case in the original specimen from the Drummond Island boulder. The first stage in the decomposition or " suissuritization " of the plagioclase shows a cloudiness due to the development of a dull, fine grained, more or less opacjue material, with a higher index of refraction causing the granules to stand out in relief from the surrounding felspar. In many cases, even in the thinnest sections, this is beyond the highest power of the microscope to resolve into its component min- eral or minerals. This is accompanied, or immediately followed, by the ^ development of sericite (hydrated inuscovite) in small scales showing characteristic brilliant interference colours. The cleavage planes and y fissures are seen to contain large scales and plates of this mineral, while certain other cracks and fissures are filled with chlorite and serpentine ' resulting from the decomposition of the bisilicates present. The smaller granules now coalesce and form larger masses and individuals of zoisite and epidote, while larger plates and scales of sericite are developed and the original plagioclase is finally replaced by a comparatively coarse grained aggregate consisting of zoisite, epidote, sericite, chlorite, calcite, and felspar. Where the alteration 'las been extreme, as in the case of the plagioclase originally piesent in the matrix of the Pogamasing specimen, the lime is more or less completely removed, and the alkaline porlim of the plagioclase has crystallized into pure limpid grains of > albile which seldom show twinnmg striations and are accordingly fre- quently mistaken for quartz with which they are often as ociated. The larger phenocrysts very frequently showed a marked difference botli in the degree and character of the alteration of their central and peripheral portions. The zoisite and epidote were much more abund- ant in the zone or belt immediately surrounding the crystals, while muscovite is the prevailing decomposition product present in the can- I / 4 i ! I ) f 4 On Somk Dykrs Containing Mukonite. "80 tral portion. In the plagioclase of the matrix the decomposition pi:;- ducts are frequently grou|)ed totether in the central pcriion, leaving a » comparatively clear and fresh periphery. Certain of the crystals ol ' felspar are quite fresh and glassy, having for some reason escaped the alteration to which most have been subjected. With the single excei)tion, perhaps, of the plagioclase originally ) contained in the fine-gramed portion of the rock from Pogamasing the I decomposition has not been of such extreme character that secondary ( albite has resulted and in every other instance the clear felspar sub- I stance is certainly an unaltered survival of the original individual. The plagioclase of thegroundmass is usually in more or less elongated forms, but occasionally mutual interference has produced at times rounded contours. In composition — to judge from the measurements of the angle contained between the maximum extinction of adjacent lamellae — the plagioclase appears to be always near the basic end of the felspar series. Some of the angles obtained are high enough for anorthite, the most basic of the felspars, but generally the angles obtained indicated labradorite as the most frequent source of the Huronite. PETROGI^\PIIICAL DKSCRIPTION.S. I. Locality. — At Hudson's Kay Co.'s Post, Bear Island, Lake Temagami, District of Nipissing, Ontario. (From a boulder.) In the hand specimen the rock is a dark green, medium textured . . diabase in which numerous large phenocrysts of plagioclase are deve- loped. Most of these porphyritic crystal' are more or less rounded owing to magmatic corrosion, although occasional individuals exhibit tolerably sharp and perfect crystallographic boundaries. Some of the crystals measure as much as three inches in diameter, but as a rule they vary from one to two inches across. They have in general a greenish tinge, although portions of some of the crystals show a flesh red colour. Most of this plagioclase is remarkably fresh and glassy, but the cleavage planes are very frequently coated with such alteration products as ser- . pentine and chlorite derived from the decomposing bisilicates present in the matrix. The phenocrysts are often seen containing or invaded by portions of the finer-grained groundmass. This matrix weathers brownish or yellowish owing to the oxidation of the iron present, while ( % The Ottawa Naturalist. the phenocrysts of plagioclase become a dull greyish white, thus ren- dering the rock very conspicuous. In general the rock bears a very close megascopical resemblance to the diabase originally described as con- taining the Huronite while the phenocrysts themselves differ only in the degree of alteration they have undergone. The writer regards this diabase as the least altered representative of the series of rocks studied but which, under similar conditions, would have furnished a rock dif- fering but slightly, if at all, from any of the more decomposed speci- mens first noticed and described as containing " Huronite." An analysis of a portion of one of the least altered of these pheno- crysts ol plagioclase, kindly undertaken by Dr. Harrington of McGill University, proves the species to be labradorite. The followiug are the results : Silica 5419 Alumina 28 "42 Ferric Oxide 077 Ferrous Oxide o ' 4 1 Manganous Oxide Trace Lime . 1047 Magnesia 052 Soda 4 47 Potash 0-63 Loss on ignition '59 10047 The specific gravity of carefully selected fragments with the bottle was 2 679. Under the microscope the rock is seen to be a very typical and rather fresh olivinediabase. In many instances the large phenocrysts are quite tresh and give the extinction angles characteristic of labra- dorite. Very often, however, irregular areas and patches have under- gone considerable " sericitization," the resultmg scales of hydrated mus- covite being very mmute. Occasionally this alteration is carried farther and both zoisite and epidote are present in addition to the sericite as a result of secondary action. At times a narrow border surrounding those crystals exhibits a micro-perthitic structure. A careful examination ad- duced sufficient evidence to indicate clearly that a more extended alter- On Some Dykes Containino Huuonitk. 35 I 1^ lion of t'.icse phenocrysts of labradorite would produce the so called Huronue. The fine-grained portion of the rock in which these crystals have been developed is a fresh aggregate composed chiefly of plagio- clase (labradorite), augite and olivine. The ophitic or diabasic struc- ture is very pronounced. The plagioclase is usually idioniorphic form- ing an interlacing network of lath-shaped crystals, the interstices ot which are filled with augite and olivine. The augite possesses the red- dish colour and pleochroism so common in diabase, the larger grains showing frequent distortion and occasional dislocation. Both the fel- spar and augite exhibit undulatory extinction as an effect of pressute. The olivine, as usual, occurs in irregular, more or less rounded ii.di- viduals, only very rarely presenting sharp crystallographic outline. Com- monly, it is rather fresh, showing a colourless or light greenish sec- tion with characteristic high relief, rough surface and brilliant mterfer- ence colours. It is rarely so fresh, however, as to be without traversing '^'^sures filled with more or less opaque alteration products. In many it mces the original olivine grain is represented by a greenish or yel- lowish material, probably serpentine. Small scales or grains of opaque iron ore (magnetite) are associated with this serpentine indicating that they were also a result of the decomposition of the olivine. Less fre- quently, perhaps, the olivine shows a very interesting and rather un- usual alteration to talc, but the resulting scales of this mineral were so small that this could not be ascertained beyond dispute. The talc is of a very pale green colour, slightly pleochroic, and exhibits very brilliant mterference colours between crossed nicois. It occurs as a matted or felted aggregate of very minute scales filling the original olivine grain. The talc is usually accompanied by more or less opaque iron ore and occasionally some chlorite, (i) A considerable quantity of biotite is present which in some cases has undergone considerable ''bleaching" owing to the removal of iron, while in other cases it is altered to chlorite. Apitite is also a tolerably abun- dant accessory constituent. The magnetite occurs usually in irregu- lar black grains, most of which have resulted from the decoir.posi- « (l) Vol. III. Geo!., VVisconsin, p. 235. 36 The OrrxwA Naturalist. tion of the olivine. Frequently, however, it occurs in tabular or rod- like forms, which are sometimes arranged in one set of parallel |ilanes only, while in other cases ^hey lie in two sets of planes intersecting one another. These rod-like forms penetrate all the constituents of the ' rock. In many instances the smaller rod-like forms occur in associa- tion with the biotite, and their correspondence in position with the planes of cleavage of this mineral suggests that in these cases, at least, their formation has been due to secondary action (" Schillerization "), in- volving the elimination of the iron and the development of magnetite along the planes of easy cleavage. 2. Locality. — S.E. \, N.W. \, Section 19, 65, 3, cutting on the Port Arthur, Duluth and Western R.R, j ist west of the narrows of Gunflint Lake, Minnesota, (i) Mr. U. S. Grant, who kindly sjnt me the specimen', at Prof. Win- chell's request, says: "The rock is from one of the diabase sills (2) in the lower oriron-bearing memberoftheAnimikie. '\ he markedly porphyritic character is only local, the main part of the sill being without phenocrysts. These porphyritic |)atches are sometimes rather sharply marked off from the main mass of the sill, but they usually pass into the non- porphyritic parts simply by a gradual loss of the large crystals. This sporadic development of large felspar phenocrysts in certain of these Animikie sills is a rather common feature." Macroscopically the rock resembles very closely the boulder brought from Lake Temagaiui, bemg a dark groen diabase with pheno- crysts of fresh plagioc!ase which exhibit the polysynthetic twin lamel- lation very beautifully. '^ . . ■*" The microscope reveals a rock composed mainly of plagioclase and augite with pronounced ophitic structure. The augite when fresh is of the reddish and slightly pleochroic variety so common in diabase, but it shows abundant alteration to greenish or brownish green hornblende (uralite). The opaque iron ore has the same rod-like development noticed in the examination of the preceding rock. Biotite is i)resent w (i) Specimen No. 951, Geographical ami Natural History .Survey of Minnesota, collector U. S. Grant, see 22nd Annual Report, p. 82. {2) Logan hills of Lawsou, see L'ulletin 8, .Minne.'ota .Survey. On Some Dykes Containing IJuronitk. 3; W and shows considerable "bleaching" and chloriiization. The larger phenocrysts, which are probably labradorite, are mostly quite fresh and glassy, but irregular areas are more or less clouded by the development of minute scales of sericite or kaolin. The rock differs from the Temagami specimen in the absence ot olivine and the advanced uralitization of the augite. 3. Locality. — Landing at Silver Islet, north shore of Lake Superior. Prof. Winchell thusdescribes this rock (601) : (i) 'A coarse porphy- ritic 'dioryte'in a dyke running parallel to and contiguous, to and passing into (602) a fine grained 'dioryle' in the form of a dyke. The interval of transition is perhaps two feet wide, and th j crystals of felspa*" are scatteringly disseminated through it on the south side, and wholly disappear on the north side. They run in the same direction as the dyke on Silver Islet. The whole is 45 feet wide, but is evenly divided between Nos. 601 and 602 from about a mile north of the ' Landing at Silver Islet.'" The thin section under the microscope showed an aggregate of plagioclase (labradorite), augite, serpentine and opaque iron ore. The phenocrysts of plagioclase as well as the lath-shaped crystals pre- sent in the groundmass show more or less ' cloudiness ' due to the development of minute scales of muscoviie. Irregular fissures travers- ing the felspar aie filled with yellowish green serpentine derived from that present in the surrounding matrix. The augite, which is quite fresh, has a reddish colour, and is slightly pleochroic. It occurs in irregular grains and areas filling in the spaces between the plagioclase laths. The yellowish green serpentine, which is abundant, is present in areas whose external form and internal arrangement at once suggest its alteration from olivine, which was no doubt originallv present. These phenocrysts of labradorite are much fresher than those to which the name " Huronite '' has usually been applied, but under similar conditions of alteration there is no doubt that they would become so decomposed as to be indistinguishable from this mineral. (i) Specimens Nos. 601 and 602, loih Annual Report of Geological and Natural History Survey, Minnesota, page 56. as TiiK Ottawa Natukalist. 4. Loca iit v. — Knoh or Fault Hill, west branch HanuUon River, 20 miles below old Fort Nascawpee on L.ake IVlitsikpo v, (i) Labrador Peninsula. The specimen, according to Mr. .\. \\ Low, is from a dyke cutting the ferruginous limestones and shales of Knob or Fault Hill, a promi- nent topograi)hical feature, as it rises rather abruptly to tlie height of 350 feet above the surrounding country. The dyke occupies the sum- mit of the hill, while 200 feet below come in the stratified rocks through which it has been intruded. Neither the width of the dyke nor the nature of its contact with the bedded rocks could be ascertained owing to the accumuhtion of drift material, but it certainly cannot be much less than 200 yards. Macroscoi.ically the hand specimen shows a medium textured dark green almost black diabase containing occasional small and imperfect phenocrysts of a light greenish grey plagioclase which has undergone incipient "saussuritization." Under the microscope the rock is seen to be composed of an aggregate of plagioclase, augite, serpentine, and ilmenite. The augite is very fresh, has a light brownish red colour and shows a marked pleochroism. In general its foim is allotriomorphic, filling in the spaces between the felsjiar, but occasional individuals exhibit sharj) and perfect crystal boundaries. The plagioclase occurs in more or less elongated lath-sha[)ed crystals which are often somewhat stout and rounded thus producing a rather coarse ophitic structure. Many of the small individuals are quite fresh, but the larger ones show considerable alteration to sericite and epidote. The resulting " saussurite " is in no instance so abuntlantly develojjcd as to destroy the polysynthetic twinning striae The large amount of serpentine noticed in this rock has evidently resulted from the decom- position of olivine originally present. The serpentinization of theolivme is in every instance completed, and only the outline and structui of the serpentine individuals serve to indicate the mineral from which it has been derived. These occasionally show a network of fibrous ser- pentine which was first produced, the greenish fibres standing perpen- dicular to the cracks along which they have been developed. Owing »■■' (i) Reference No. 4, A, p. 28, IJook II., Low, 2i/(')/94. * / On Some Dykes Containino JfUKoNiTK, SO i *f to this parallel arrangement of the fibres, the serpentinous substance gives a faint but definite reaction with polarized light. The meshes of the net-like structure thus produced are filled with more finely devel- oped scales and fibres of serpentine which are nearly, it not, quite isotropic. These decoivposed grains are often seen embedded in the fresh augite. The ilm^nite occurs in large irregular fragments or in small more or less rounded granules and in both cases shows character- istic alteration to leucoxene. The leucoxene is of the usual opaque grey colour, but sometimes brownish grey, and frequently show, especially in the thinner portions of the slide as also the smaller frag- ments, the brilliant chromatic polarization of sphene of which it -.s simply a vari^jty. 5. Locality.— Yi^ mile north of Murphy Lake, Timber Limit, 90, District of Algoma, Ont. The specimen is from a dyke cutting rocks of Huronian age. The matrix is a normal dark green diabase whose ophitic. structure is mega- scopically apparent. A freshly exposed surface shows the Huronite to be of the usual pale yellowish green colour, while the less altered por- tions of the crystals have a more or less pinkish or flesh red colour. In many of these individuals a somewhat indistinct cleavage and a rather faint striation due to multiple twinning may be seen. The matrix weathers a brownish colour while the phenocrysts become a dull opaque greyish white thus rendering portions of this rock which , have been subjected to atmospheric action very conspicuous. Microscopically, the Huronite is seen to be labradorite which has { undergone more or less " saussuritization." A narrow border usually surrounds these phenocrysts of labradorite which is free from the pro- ducts of decomposition, but immediately within this rim is a zone or band where the alteration has been extreme and here the resulting '^ zoisite, epidote and sericite replace nearly, if not quite, all of the origi- nal felspar. The epidote and zoisite are present in irregular grains or masses, while the sericite, as usual, occurs in scales and plates. All of these alteration products have a more or less definite arrangement. The grains and imperfect crystals of epidote and zoisite are usually elongated in a direction corresponding more or less with the twinning striations 40 The Ottawa Naturalist. or in a direction nearly at right angles while the scales and plates ot sericite have a similar dev'elopmcnt. The specific gravity, ascertained by Mr. R. A. A, Johnston, of these porphyritic crystals was 2758. The matrix of these crystals is a rather fresh dir-base with pro- nounced ophiiic structure and composed chiefly of plagioclase and augite. The plagioclase is idiomorphic and forms an interlacing net- work of lath-shaped crystals. Occasional crystals are rather fresh and glassy, but usually they exhibit the same alteration as the larger por- phyritic individuals, and apparently belong to the same species of felspar (labradorite). The decomposition products aggregate themselves to- ward the centre of the crystal leaving a somewhat fre; h perij^hery. The augite is in general quite fresh, bat occasionally an individual was seen partially altered into green, strongly trichroic hornblende. Twins are common. A considerable (piantity of biotite is present wiiich is al- ways more or less altered to chlorite, llmenite, an abundant consti- tuent, occurs in irregular grains and only shows incipient alteration to leucoxene. Occasional prisms of apatite were noticed, chiefly developed in the chloritized biotite. The more unaltered portions of the plagio- clase show the undulatory extinction due to pressure. Pyiite is also an abundant constituent. 6. Locality. — Algoma Mills, north shore of Lake Huron, district of Algoma, Ontario, (t) The thin section exhibits a rock very similar to the one just des- cribed and must be regarded as being derived from a dyke almost anal- agous in character and composition to that exposed near Murphy Lake. The phenocrysts of labradorite show the usual alteration into an aggregate composed chiefly of muscovite, epidote and zoisite although considerable portions of some of the crystals are free from these de- composition products. The augite has a light yellowish colour and is only slightly pleochroic. Twins are common, the twinning plane and composition face being the orthopinacoid. Curved or distorted individuals were often noticed exhibiting the *F"rom a boulder No. 1605, Geological Survey of Minnesota, series of rocks, i8th Annual report, j-age 58. On Some Dvkks CoNTAiNisfi Huromtk. #1 " 'train shadows" due to pressure. A good proportion showed an in- cipient uralitization. The plagioclase of the groundinass has also undergone more or less "saussuritization " and occurs in stout and roundeil laths thus producing a rather coarse ophitic structure. 'I'he ilmenite present in irregular grains is often fresh but shows occasional incipient alteration to leucoxene. A small amount of chlorite is also present. 7. Locality — Shore of Drummond Island, Lake Huron, (from a boulder.) The slide was made from a fragment, obtained through the kind- ness of Dr. Harrington, from a dui)licate specimen of the original boulder at present in the Holmes collection of the Peter Red|)ath Mu- seum of McGill University. The first examination and analysis by Dr. Thomson was rather imperfect as pointed out by Dr. Harrington (i) but it ha3 been thought advisable to reproduce the analysis, though im- perfect, for purposes of rough comparison. This analysis is as follows : Silica 45 ■ 80 Alumino 33 92 Ferrous Oxide 4 3^ Lime 8 ' 04 Magnesia 172 Loss on ignition 4. 16 9796 The specific gravity, according to Dr. Thomson, is 2-8625. Under the microscope the phenocrysts of the so-called " Huronite " are seen to be a decomposed aggregate of zoisite, muscovite, efjidote, calcite, chlo- rite and felspar. Occasionally there is a very narrow border of compa ratively unaltered felspar surrounding these individuals, in which traces of the very fine striation, due to multiple twinning, may be observed. Im- mediately within this band, however, the decomposition products are most abundant, and the original plagioclase is replaced almost altogether by epidote, zoisite and muscovite, their relative abundance being in the order mentioned, while the interior of the crystals is composed mainly of muscovite with a much less proportion of zoisite, epidote and felspar. (I) Trans. Royal Society of Canada, vSeclion IIL, 1886, p. S2. . i k 42 The Ottawa Naturalist. The epidote and zoisite occur in irregular, often somewhat elongated masses or "grape-like " bunches which frequently show a more or less definite arrangemenr in accordance with the structure of the original felspar. Both minerals exhibit theit characteristic high relief, the epi- dote showing brilliant chromatic polarization colours, and yellow to colourless pleochroism, while the interference colours of the zoisite, as usual, are very low, dull bluish to yellowish. The sericite is of a very pale green, and occurs in scales or aggregates of scales and plates, show- ing customary brilliant polarization colours and parallel extinction. The sericite has, likewise, often a definite arrangement, but sometimes occurs in irregular or matted aggregates. The " saussuritization " of the origi- nal plagioclase has been usually so complete, that only traces of the winning lamella can be detected. The matrix in which these crystals are embedded is a diabase, composed essentially of plagioclase and augite. The plagioclase shows moie or less alteration, identical in cha- racter with that of the larger phenocrysts so that it must have had a similar composition. It occurs as lath-shai)ed, twin crystals, often con- sisting of only two lamellae, which pierce, and are often embedded in the augite. The augite occurs in more or less irregular masses, filling in the interstices between the felspar laths. It is light-brownish in colour, exhibits a faint pleochroism, and the characteristic interrupted cleavages in cross-section. It is partially altered into green trichroic hornblende, and occasionally the alteration has been carried so far that chlorite has resulted. This uralitization has only proceeded to a limited extent, and is confined to a narrow margin surrounding the irregular fissures traversing the augite masses. Occasional twins were noticed, the twinning plane being the orthopinacoid. Ilmenite is abundant, but almost wholly converted into leucoxene. The fragments have generally jagged and irregular contours, but occa- sionally, some are seen which possess a rather perfect crystallographic outline. The characteristic alteration along lines parallel to the faces of the rhombohedron produces alternating bands of greyish white leu- coxene, and black, unaltered ilmenite. The less altered portions of the plagioclase and the augite show uneven or wavy extinction, the " strain shadows " induced in the latter being especially well marked. On SoMK DyKKS CoNTAIXINfS HUltONITR. 43 and is a noticeable and interesting feature in connection with the rock. Additional evidence of |)rcssure is furnished by the freijuent distortion and even dislocation of both the plagioclase and augite individuals. 8. Locaii/y. -:\h()\x\. 4 miles N.W. Poganiasing Station, main line, Canadian I'acilic Railway, Dislnci of Algoma, Out. The specimen was obtained from a dyke, cutting the granitoid gneisses of the I.aurentian. The phenocrysts of " Muronite" have generally a rude, rounded outline, the largest of which are about two inches in diameter. Many of the smaller ones have irregular or jagged outline, and occasional individuals exhibit some of the sharp faces of the original crystal. The mineral is of the usual light, yellowish green colour, shows the glistening surfaces of the indistinct cleavage and occa- sional faint-striai. It is sub-translucent, has a waxy lustre, and a some- what "soapy " feel. According to Dr. Harrington* " the hardness is 5^ •Trans. Royal .Sue. Canada, .Sec. Ill, 1886, p. 82. or a little over, fusibility about 5, and specific gravity 2 '8 14." An analysis of some of the material composing these phenocrysts was made by Mr. N. N. Evans, of McGill University, for Dr. Harrington, with the follow- ing results : Silica 4707 Alumina 32 " 49 Ferric Oxide o ' 97 Lime I3'30 Magnesia 022 I'otash 2-88 Soda 2 ■ 03 Loss on ignition 272 10168 The matrix in which these crystals are developed is a fine-grained dark green diabase, with abundantly disseminated particles of iron pyrites. Uuder the microscope the "Huronite" is seen to consist of an aggregate of epidote, zoisite, sericite and chlorite, but in the larger crystals especially, considerable areas of unaltered plagioclase exist which are quite fresh and glassy, and exhibit the twinning lamellae quite distinctly. The smaller phenocrysts, however, are altogether < k w; 44 TiiK Ottawa Natuhalimt. dccoinposod so tliat there is little or no evidence of the lamellation of the original felspar. The matrix in which these crystals arc embedded is an exceedingly decjmpoied gro ladm.iss made up of felspar, epidote, chlorite, hornhlende and zoi>ite, with larger individuals of augite in a more or less advanced sta^e of uraliti/.ation. 'I'lie alteration to horn- blende is mainly marginal and has ])roceeded very imevenly, the core of unaltered augite, having thus a very irregular in which cores of the original augite are still present. The ilmenite present is more or less altered to leucoxene showing brilliant polarization colours (compare No. 8 ante). A considerable amount of biotite of a light brown colour on account of the "bleaching" it has undergone shows rather brilliant inlerfetence colours. The biotite has also been altered in many cases to chlorite, (iranophyre structure was also noticed. //. Locality. — Lake Petitsika|»ow, about 15 miles below old Fort Nascawpee. West branch Hamilton River. Labrador Peninsula. (2) The dyke from which the sample was taken, according to Mr. Low, is 200 yarJs in width, coarsely crystalline in the centre where the porphyriiic individuals of Huronite are often three-fourths of an inch in diameter. The dyke breaks through and alters sandstones, limestones '^ (i) Williams' Appendix I., I'tirt P\, Annual Report, Geological Survey of Canada, V'ul. V., 1889-90, p. 60. (2) Reference No. 4, p. 3c, lik. II. Low, 23/6/94. On Some Dykes Containing Hlronitk. 47 and shales of Cambrian age, running almost parallel to their strike. The specimen was taken from near the middle of this dyke, and shows macroscopically a dark preenish grey, rather coarse grained diabase, in which are embedded numerous phenocrysts of altered greenish felspar (Huronite). The crystals of " Huronite," thou^iJ uch smaller than usual, are on the other hand much more abundant, so that it is otten difficult to obtain even a small chip of the finer groundniass, in which they are embedded. The felspar of both the larger porphyritic indi- viduals and those present in the groundmass show great alteration, althoug the polysynthetic twinning lamellce may still be recognized. The decomposition products are mainly sericite and epidote. The specific gravity of these phenocrysts according to Mr. Johnston, is 2- 7 73- The aiigite when fresh (which is rarely the case except m very minute fragments), is of a reddish colour, and shows distinct pleochroison. A great deal of chlorite is present. The ilmenite occurs in irregular grains as well as fragments, which have a more or less perfect crystallographic outline and occasional perfect rhombohedra were noticed. The alteration to leiicoxene is very characteristic, this resulting form of sphene frequently exhibiting its characteristic brilliant chromatic polarization in thin sections, (i) Besides these larger frag- ments small rounded grains of a brownish grey translucent mineral occur with high index of refraction, and show brilliant interference colours. These occasionally show small granules in the centre of un- altered titanic iron ore, and thus reveal their derivation. Apatite is very abundant, and occurs in colourless prismatic needles which are frequently bent, cracked and broken. Pyrite is also a rather abundant accessory constituent. ' (l) Page l6 A, Report Geological Survey of Canada, 1880-2.