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 LIBRARY 
 
 UNIVERSITY OF 
 CALIFORNIA 
 
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 SCIENQGt 
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 LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 GIFT OF" 
 
 Class 
 
A STUDY OF 
 
 THE IGNEOUS ROCKS 
 
 YORK HAVEN and STONY BROOK, PA. 
 
 THEIR ACCOMPANYING FORMATIONS 
 
 THESIS 
 
 Presented to the Faculty of the Department of Philosophy of the 
 
 University of Pennsylvania, in partial 
 fulfillment of the requirements for the degree of Doctor of Philosophy 
 
 BY 
 
 FREDERICK EHRENFELD, A. B. 
 
 PHILADELPHIA 
 
 PHILADELPHIA 
 AVIL PRINTING COMPANY 
 

 E4 
 
 EARTH 
 
 SCIENCE 
 
 LIBRARY 
 
INTRODUCTION. 
 
 The American Triassic in the region of the Atlantic 
 border States is, as is well known, pierced by numerous 
 igneous eruptions throughout its entire area. One has 
 only to turn to the literature of the Triassic area from 
 Massachusetts to North Carolina to obtain an idea of the 
 great numbers of these dikes and the variations they show 
 in length and thickness. From thin sheets of a few inches 
 in thickness we find all gradations up to several hundred 
 feet in thickness and many miles in length. 
 
 Furthermore, the forces which produced these eruptions 
 in the Trias by no means confined themselves to the rocks 
 of that age, for the surrounding formations down to the 
 Archaean are characterized in many places by eruptions 
 which are no doubt intimately connected with those of the 
 Trias itself. 
 
 In spite of the great distance apart of many of these 
 eruptions, their lithological character is in general the 
 same. They all, or nearly all, fall into one or other of the 
 types known as dolerite, gabbro, diabase, or the alterations 
 thereof. 
 
 In Pennsylvania the area of these eruptions extends in a 
 southwest direction from the New Jersey line through to 
 and including York and Adams counties to the State of 
 Maryland. On the map of York county, published by the 
 Second Geological Survey of Pennsylvania, ten or more of 
 these dikes have been indicated. These have been described 
 in a general way in the various reports on York and Lan- 
 caster counties. 1 Persifor Frazer discusses 2 the traps of 
 
 1 See Reports C, CC,and CCC . Second G. S. Pa. 
 
 2 Second G. S. Pa. Report C, pp. 115-129. 
 
 (3) 
 
4 
 
 York and Adams counties, and refers them all to dolerite. 
 With this exception little if any work has been published 
 in regard to them. 
 
 The following investigation was begun with the desire of 
 studying two of these dikes in order to ascertain what 
 points of resemblance or difference they might show with 
 similar regions elsewhere. In addition to this work a 
 study was made of the formations surrounding one of these 
 dikes. 
 
 The two localities selected are at York Haven and Stony 
 Brook, both in York county. At the former locality the 
 surrounding rocks are Triassic, at the latter they are 
 Cambrian. 
 
 Before proceeding to a description of these dikes it may 
 not be amiss to indicate briefly the geological structure of 
 the part of York county referred to. 
 
 The accompanying map, which is reduced from the 
 State Survey map of York county, will assist in making the 
 geological structure clear. 
 
GEOLOGICAL STRUCTURE OF THE REGION. 
 
 In passing across the county in a southeasterly direction, 
 or in following the course of the Susquehanni River, the 
 formations present themselves in the following order :* 
 
 New Red Sandstone, 
 
 Siluro-cambrian Limestone, 
 
 Hydro-mica Schist, 
 
 Quartzite, Potsdam, 
 
 Chlorite Schist, 
 
 Azoic Slates. 
 
 By the geologists of the First Pennsylvania Geological 
 Survey, 1858, Henry D. Rogers, director, the limestone 
 above mentioned was considered as equivalent to the 
 Black River, Chazy or Calciferous of New York State. 
 The quaitzite was regarded as Potsdam. When the second 
 survey of Pennsylvania was organized, Dr. Persifor Frazer 
 was put in charge of the survey of York county, and he 
 arranged the formations in descending order as given 
 above. 
 
 In 1892, C. D. Walcott, of the U. S. Geological Survey, 
 began an investigation of the supposed Silurian and Cam- 
 brian rocks of York county. The results of his work were 
 published as a Bulletin of the U. S. Survey. 2 Mr. Walcott 
 places the above mentioned quartzite, limestone and chlorite 
 schist in the Lower Cambrian, and in fact he regards it as 
 doubtful " if there is in York county a sedimentary rock 
 other than the mesozoic New Red S. S. of later age than 
 Cambrian." For details of his work reference must be 
 made to Bulletin No. 134, previously mentioned. 
 
 In regard to the New Red it is not necessary here to 
 
 iSee map of York County, published in Report Ca, Pa. Geo. Survey. 
 2 The Cambrian Rocks of Pa., by C. D. Walcett, Bull. 134, U. S. G. S. 
 
 (5) 
 
fire . Ac g 
 
 GL 
 
 M i* 
 K,Co 
 
 mention in detail what has been 
 done in this field of geological 
 research. The literature on the 
 subject is voluminous and has been 
 admirably summarized by I. C. 
 Russell. 1 
 
 In Pennsylvania the most recent 
 work is that of B. S. Lyman, in 
 Bucks and Montgomery counties. 
 From the results of his work Mr. 
 Lyman derives the following sub- 
 divisions, arranged from the top 
 downwards : 2 
 
 5. Pottstown Shales. Ten thou- 
 sand seven hundred feet of shales, 
 mostly soft and red, with a few 
 beds of limestone. Fossils are ob- 
 scure plant remains and the Dino- 
 saur Clepsaurus Pennsylvania of 
 Lea. 
 
 4.. Perkasie Shales. Two thou- 
 sand feet of dark red, gray or green 
 shales. The shales are in general 
 hard and have several blackish or 
 coaly layers. Fossils have not 
 been satisfactorily made out. 
 
 j. Lansdale Shales. Four thou- 
 sand seven hundred feet, more or 
 less, of shales mostly calcareous 
 and in large part red in color. 
 There are a few scattered green 
 layers and a little soft red sand 
 rock. The beds are in general 
 soft. Fossils few. 
 
 2. Gwynedd Shales. Three 
 
 The Newark System, by I. C. Rusell. Bull. 85 U. S. G. S., 1893. 
 Summary Final Rp.P a. Geol. S. 1895, Vol. 3, \.p. 2607 et seq. 
 
7 
 
 thousand five hundred feet. These rocks are hard, fre- 
 quently very hard. Towards the top are dark red, also 
 green, gray and even black, with a little coal. From these 
 beds have come most of the important fossils of the Trias- 
 sic. Mr. Lyman places these beds as equivalent to those 
 of the Richmond, Virginia, and North Carolina exposures. 
 (See p. 2611 of the Report before cited.) 
 
 /. Norristown Shales. Six thousand one hundred feet 
 
 This series makes up the lowest members of the New 
 Red in Bucks and Montgomery counties. These rocks are 
 prevailingly red in color, particularly at the bottom. Near 
 the base also are some beds of coarse, pebbly, hard, gray 
 sand rock. Near the top are courses of brown building 
 stone. Beds of this nature are not suited for the preserva- 
 tion of fossils, and, as a matter of fact, few have been found. 
 
 " It is clear," says Mr. Lyman, " that the paleontological 
 age of this set of beds has never been satisfactorily deter- 
 mined. . . . there is a strong probability that they are 
 Paleozoic, at least as old as the Permian." (P. 2614 of Ly- 
 man's Report.) 
 
 Since Mr. Lyman's work in Pennsylvania was published, 
 Henry B. Kiitnmel, 1 of the New Jersey Geological Survey, 
 working on lithotogical evidence, has divided the Trias of 
 that State into three divisions : 
 
 Feet. 
 
 Stockton series 4.700 
 
 Lockatong series 3, 600 
 
 Brunswick shales 12,000 
 
 20,300 
 In the absence of detailed information of the character 
 
 of these beds no correlation of them with Lyman's may be 
 
 safely attempted. 
 
 During the progress of my own work in York county it 
 
 !Am. Rep. G S. of New Jersey, 1896, p. 59. 
 

 3050' 
 
 2900' 
 
 2140 
 
 __ I3 ' (24) 
 5MP3 90' (23) 
 
 285' (15-22) 
 
 go' (11-14) 
 90' (8-10) 
 
 75' (7) 
 80' (5-6) 
 'SO' (4) 
 
 8 . . 
 
 was desired to obtain an idea of the character of the Trias 
 below the dike at York Haven ; that is, in its lower part. 
 Accordingly a section was measured 
 from the contact of the Cambrian and 
 Trias up to York Haven. This is 
 indicated on the map by the line 
 A-B. 
 
 From thestratigraphical evidence as 
 well as from the fossils found, it is be- 
 lieved that the position of these beds 
 may be indicated with some degree 
 of accuracy. The thickness is in all 
 4350 feet. It is only fair to say that 
 approximate value only is claimed for 
 this section, especially the lower part. 
 The thickness was obtained by calcu- 
 lation from the dip and horizontal 
 distances. In the lower part exposure 
 is poor, in the upper part very good. 
 The lower portion for an estimated 
 thickness of 1960 feet is concealed, 
 and the character of the formation is 
 judged from surface indications, such 
 as the color and other physical aspects 
 of the soil. Near the middle of the 
 concealed portion an outcrop of dark 
 red, sandy shale was noted. The 
 soil was dark brownish red in color. 
 At a point three hundred feet below 
 this an outcrop of conglomerate was 
 seen. The pebbles were of quartz, 
 varying in size from less than an inch 
 in diameter up to five or six inches. 
 The soil contains many of these peb- 
 bles, which increase in number 
 
 So' (2-3) 
 
 1 80' 
 
9 
 
 towards the bottom. The dip at each of these outcrops 
 gave an average of 23 N. W. 
 
 At the top of this concealed part the soil is yellow in 
 color. Arkose or granitic sandstone was observed here. 
 
 Above the concealed part the rocks with a few exceptions 
 are well shown and their character was easily made out. 
 From the drawn illustration the positions of the different 
 members nruy be seen. 
 
 DETAILED DESCRIPTION OF SECTION. 
 
 The following description is intended to cover the mem- 
 bers of the section above the concealed part beginning 
 1960 feet above the bottom. The numbers refer to those 
 given in parentheses in the illustration of the section. 
 
 (1) One hundred and eighty feet of sandstone, mostly 
 fine grained and light gray in color. Fine scales of mica 
 and a little feldspar are scattered through the rock. There 
 is evidence, in places, of its having been deposited in 
 changing currents. Interspersed with these sandstone beds 
 are layers of shale. 
 
 (2) Above the sandstone are twenty feet of a soft, crumb- 
 ling red shale, containing numerous rounded calcareous 
 nodules. Fossils are obscure plant remains and forms 
 resembling some species of algae. 
 
 (3) Next come thirty feet of a quartz conglomerate, mostly 
 fine grained, but in some places rather coarse. Mica and 
 pyrite are scattered through the rock. The conglomerate 
 is of a light color, with a faint bluish tinge. 
 
 With this conglomerate are beds of fine grained, grayish 
 or brownish sandstone, with a good deal of mica and a 
 small amount of feldspar. 
 
 The formations following for an estimated thickness of 
 seven hundred feet are concealed. The soil is sandy, and 
 toward the botton is reddish in color. At the top it is 
 yellowish. 
 
10 
 
 (4) On hundred and fifty feet of a dark gray, almost black, 
 sand rock which is in places quite calcareous. Small 
 fragments of a soft, shaly material are occasionally seen. 
 The rock contains mica and some feldspar, and somewhat 
 resembles a granitic sandstone in appearance, though hardly 
 to be classed as such. 
 
 (5) This member comprises about seventy feet of shale and 
 sandstone. At the bottom are several feet of a hard, fine 
 grained green sandstone, with small scales of white mica 
 The sandstone in weathering, forms roundish blocks which 
 in their natural position resemble a wall of masonry. 
 Closely associated with this sandstone are beds of red and 
 green shales. 
 
 Following come fifty feet or so of sandstone. At the 
 bottom the beds are soft and yellow ; they pass, however, 
 into rather coarse gray or green layers, containing a few 
 particles of pyrites. Towards the top the layers become 
 fine grained and contain thin streaks of linonite iron ore. 
 
 Following are ten feet of red shale like number 2. 
 
 (6) This member comprises ten feet of fine grained yellow 
 sandstone. 
 
 The next sixty feet are concealed. The soil is sandy, 
 yellow in color, and contains considerable vegetable matter, 
 
 (7) Seventy-five feet of hard grayish sandstone, with beds 
 of shale. The next seventy feet are concealed. 
 
 (8) Forty feet of light green sandstone, fine grained. 
 
 (9) Fifteen feet of grayish, dark green and black sandy 
 shales. The shales show a strong resemblance to those 
 found in the carboniferous coal measures of Pennsylvania. 
 Ripple marks and mud-flows are evidence that the beds 
 were deposited in shallow water. 
 
 The following plant fossils were found here: Macro- 
 t&nioptcris magnifolia, Cheirolepis munsteri, Baiera munste- 
 riana, Loperia simple x-=Bambusium of Fontaine. 
 
 There were found in addition to these a few fern frag- 
 
II 
 
 ments doubtfully referred to Mertensides bullatus, a doubtful 
 species of Equisetum and fossils which appear to be roots 
 of some sort. The Macrotceniopteris is very abundant, the 
 others not so common. 
 
 It is evident that this was the site of one of the numerous 
 marshes similar to those of the Triassic coal fields of 
 Virginia. 
 
 In the general remarks on these rocks further discussion 
 will be made of these fossils. 
 
 (10) Above these beds of shale come thirty-five feet of red 
 sandstone and red shale. A few worn fragments of 
 M. magnifolia and an Equisetum were the only fossils 
 found. With the inflowing of sand and the changed con- 
 ditions, the plants seem to have died out. Few, if any, fos- 
 sils were to be seen in the rocks above. At the top of these 
 beds are fifteen feet of soft red shales, like those before de- 
 scribed. 
 
 (i i) Twenty feet of fine grained yellow sandstone. 
 
 (\2) Ten feet of red shales, soft and crumbling. 
 
 (13) Forty-five feet of massive beds of a light col- 
 ored, almost white sandstone, it is fine in grain and 
 slightly calcareous, and contains a good deal of mus- 
 covite. 
 
 (14) Fifteen feet of shaly rock, some of which is soft and 
 red like that before described ; some is harder and greenish 
 in color. There are also some beds of a greenish gray 
 sandy rock. It is very fine grained, but rather soft and 
 earthy. It is also slightly calcareous and contains mica. 
 
 The next seventy feet are concealed. 
 
 (15) Fifteen feet of red shales. 
 
 (16) Eighty feet of fine grained, compact sandstone, con- 
 taining many scales of mica. It is light yellowish to 
 greenish in color and resembles somewhat the eleventh 
 member of the series. 
 
 (17) Ten feet of red shales. 
 
I* 
 
 (18) Thirty feet of fine to coarse grained sandstone, 
 yellowish gray in color. 
 
 (19) Fifteen feet red shales, same as previous shales. 
 
 (20) Fifty feet of hard, fine grained sandstone. The 
 beds are generally light green in color, though some of 
 them are light yellow to gray. The sandstone is micaceous 
 and in general appearance and texture resembles the 
 sandstone members just previously described, though for 
 some reason it has suffered a change in color. 
 
 (21) Red shales, five feet. 
 
 (22) Eighty feet of irregular beds of shale and gray sand- 
 stone. 
 
 (23) For eighty feet the exposure is not particularly good, 
 owing to growth of vegetation. The layers seen in place 
 are made up of an exceedingly hard, compict, fine grained 
 sandstone of a dark bluish black col>r. The rock is 
 tough and when struck with a hammer rings distinctly. It 
 weathers into round, smooth boulders which at first sight 
 strongly resemble some form of trap, or at least a baked 
 rock of some sort. 
 
 There are irregular, rounded, flat makings looking like 
 obscure forms of algae. 
 
 (24) One hundred and thirty feet of light-colored grayish, 
 almost white, sandstone, lying in fine grained, compact beds. 
 Some of the layers are strongly micaceous. 
 
 A few plant remains were seen, resembling a form of 
 Equisetuin. 
 
 The beds for the next two hundred feet are concealed. 
 From what indications could be seen it is probable that a 
 large part of the concealed portion is made up of beds of 
 sandstone similar to those just described. 
 
 (25) The remaining seventy feet up to the dike comprise 
 beds of vari-colored slates and shales. These have in some 
 cases suffered metamorphism as a result of the eruption of 
 the trap. Secondary minerals, however, are but scantily 
 
13 
 
 developed, most of the action in this direction being confined 
 to alterations in color and the formation of microlites. 
 
 The presence of many cracks and joints in these rocks i 
 make it difficult to measure the dip accurately. A general 
 average of several measurements is 19 W. N. W. As this' 
 comes reasonably close to many of the dips in the lower 
 part of the section, it is probably nearly correct. 
 
 The following description will, it is hoped, give an idea 
 of the general character of these beds. ^It was intended at 
 first to make a detailed study of thfse rocks, chemically 
 and microscopically, but lack of time did not permit. 
 Further work will be done on them later. 
 
 The first eighteen to twenty feet above the member last 
 described are made up of black, hard and brittle beds, with 
 a number of layers of gray shale. These rocks are 
 cracked and broken into irregular blocks. 
 
 Following come six feet of rock in general like the 
 former, but having many streaks of a serpentine colored 
 material. These greeni>h layers become more abundant at 
 the upper part, and pass into a whitish shaly rock. These 
 beds alternate with more greenish rock. 
 
 Next comes a rock which is rather persistent, occurring 
 in several different beds. It is hard, blackish, with a faint 
 blue tinge. It is brittle and has a fracture like that of slate. 
 
 On the surface it is spotted with grayish black marks. 
 A microscopic examination revealed the presence of very , 
 minute dust-like crystals of magnetite. These are scattered 
 pretty uniformly through the rock, but they have frequently 
 crowded together to produce rounded opaque spots. 
 
 This gives the general appearance of a volcanic glass in 
 which swarms of microhtes have appeared, though of 
 course this rock has not the glassy character. (For illustra- 
 tion see plate, Fig 2.) 
 
 The remaining rocks are mostly green, black and pink 
 shales or slates. A common rock is a light ytllowish green 
 
shale. Microscopically it is seen to consist of fine grains 
 lying in a base, which in ordinary light is clear and color- 
 less, but which polaiizes to a gray blue with a few patches 
 of yellow. A high power shows the presence of many fine 
 transparent needles, which polarize with parallel extinction. 
 This rock has layers in which are crowded together many 
 small crystals of apatite. (See plate, Fig. i.) This rock occurs 
 within twenty-five or thirty feet of the lower side of the dike. 
 
 GENERAL REMARKS ON THE RELATION OF 
 THE ROCKS. 
 
 It will be noticed from the description given of the rocks 
 in the section measured that, excluding the lower part, 
 which is concealed, the prevailing character of the rock is 
 a fine grained sandstone. Shale is not very abundant aside 
 from the thin beds of the soft red shale. Of course, in 
 regard to the lower .part there is doubt as to the character 
 of a large part of it. It must be considered, also, in the 
 upper part, that those portions of the column which are 
 concealed are in general lower in elevation than the parts 
 which are well shown. This would indicate soft rocks, such 
 as shales. Still, in spite of this, it seems safe to say that 
 the greater part of the formation is composed of sandstone. 
 
 Now, in the region of Bucks and Montgomery counties 
 in Pennsylvania, the researches of Lyman have shown that 
 the greater part of the formation is shale, excepting the 
 lowest members the Norristown division. On the other 
 hand, in Virginia and Maryland coarse conglomerates and 
 large stones or groups of stones occurring in the finer sand- 
 stones are remarkable features of the formation. 1 
 
 From this it would seem that the formation in York 
 county occupies an intermediate position between the beds 
 in Bucks county and those in Virginia. For if the material 
 came from the south, the larger part, such as boulders, 
 
 1 Dana's Manual, 1895, p. 745. 
 
15 
 
 would be left near the source, while the clays and muds 
 would be carried furthest. That the formation in this part 
 of York county is of the same age as that further south is 
 indicated by the fossils which were named on a previous page. 
 
 B. S. Lyman has attempted a correlation of the fossils 
 of the Trias. 1 He places all the important plant fossils, such 
 as those occurring in Virginia, towards the bottom of the 
 Gwynedd shales, the second division in the New Red of 
 Bucks and Montgomery counties. Thus in Hanover and 
 Cumberland counties, Virginia, occur Macrotceniopteris 
 magnifolia, Cheirolepis munsteri, Equisetum rogersi, etc., 
 which are the species found below York Haven. 
 
 From this it would seem that the formations here studied 
 belong in the lower part to the Norristown shales of Ly- 
 man's division, and extend in part into the Gwynedd. Certain 
 fossils found in York county, at Goldsboro several miles 
 above York Haven, are referred doubtfully to the Lansdale 
 beds by Lyman. 2 
 
 In the absence of cross sections connecting the lower and 
 upper beds in York county, any speculations regarding 
 their relative positions are of questionable value. A general 
 section might be constructed across the county from the 
 observations already published, but it would be of no value. 
 
 The remainder of this paper is given up to a description 
 of the two dikes mentioned in the introduction, beginning 
 with the one at Stony Brook. 
 
 THE STONY BROOK DIKE. 
 
 By reference to the map the position and length of this 
 dike may be seen. It is about twelve miles long, beginning 
 in the Cambrian limestone east of York, and running south 
 through the slates and schists indicated on the map. 
 
 1 Proceedings Am Phil. Soc., vol. 33, pp. 204215. 
 
 2 See Pa. Geo. S. An. Report, 1887; also, Summary Final Report, vol. 3, p. 2610. 
 
i6 
 
 Its course maybe traced by the trap rubbish along the sur- 
 face. It has been referred to by Persifor Frazer as the 
 Loganville dike. 1 
 
 . It is here called the Stony Brook dike, since the most 
 important exposure of it is in the cut of the Frederick 
 Division, Pennsylvania Railroad, at the village of Stony 
 Brook, four miles east of York. 
 
 It was hoped that at the village of Enterprise, on the 
 Peach Bottom Railroad, southeast of York, where there 
 runs a branch of the Codorus Creek, the dike would be 
 exposed in its natural position. Such is not the case, 
 however; consequently, no evidence of metamorphic action 
 of the trap was found. Numerous trap boulders occur, 
 mingled with fragments of quartzite and chlorite schist. 
 
 The interesting fact was noticed here that some of the 
 boulders when struck possessed great resonance. Of 
 two pieces lying side by side, one when struck rang 
 almost like a phonolite, while the other did not have this 
 property. As the fragments were seemingly alike in all 
 other respects, the difference was probably due to some 
 difference in their position in the ground. 
 
 At the railroad cut at Stony Brook the dike is well exposed 
 and its width easily measured ; it is seventy-four feet wide. 
 Its contact with the limestone is sharp and distinct. At 
 this point the dike makes a small elevation, which soon 
 fades away. The limestone adjoining the dike is highly 
 crystalline, but contains no secondary crystallizations of 
 minerals. It is whitish in color, with thin blackish streaks. 
 There are also some thin beds of shale. 
 
 Perhaps the most striking feature of the limestone here 
 is a layer of conglomerate, differing from ordinary rocks 
 of this name in the fact that the material is all limestone. 
 It has probably resulted from the cementing together of 
 limestone pebbles and fossils, which have since been altered 
 
 1 Report C, Pa. Geo. Survey, p. 95. , ,v> -.. : 
 
17 
 
 by metamorphic action. Persifor Frazer has mentioned the 
 occurrence of a similar conglomerate near Columbia, Penn- 
 sylvania. 1 This limestone conglomerate appears to be a 
 somewhat common occurrence in the older limestones , of 
 Pennsylvania. C. D. Walcott has called such formations 
 " Intraformational Conglomerates," 2 and in his report on 
 York county, before mentioned, he figures such an occurr- 
 ence near York. 
 
 Prof. J Peter Lesley, in speaking of this dike, and one 
 west of York, says : 8 " In this case, as in that of the Gon- 
 shohocken, Montgomery county, Pa., dike, no production 
 of white marble appears as due to igneous action." This is 
 beyond all doubt true, as at many localities in this same lime- 
 stone belt, at wide distances apart, fine grained white marble 
 appears where there is no evidence at all of igneous action. 
 In fact, in York county the limestone shows great varia- 
 tion, ranging fiom a hard, compact limestone to a fine white 
 marble. In some places all gradations from one form to 
 the other may be observed. 
 
 The metamorphism is regional and not local, and proba- 
 bly occurred long before the trap was erupted. 
 
 It may, however, seem strange that the limestone at the 
 junction of the dike shows no evidence of igneous action. 
 Toe composition of the limestone, as shown in the following 
 analysis, should be sufficient to explain this : 
 
 ANALYSIS OF LIMESTONE FROM STONY BROOK. 
 C*CO 3 ........... . . 96.61 
 
 MgCO 3 ............. 1.40 
 
 StO 2 .............. i.oo 
 
 Carbon 
 
 1 Pa. Geo. Survey, ReportC, p 132. 
 
 * Bull. Gco. S Amer., vol. 5, pp. 192-98. 
 
 8 Summary Final Report, Pa. G. S., 1892. p. 454. 
 
18 
 
 It will be observed that the percentage of MgO, SiO 2 , etc. 
 is small not enough, in fact, to allow the formation of 
 secondary minerals in the limestone. The minerals usually 
 found in such instances are those like the amphiboles, garnets, 
 andalusite, pyroxenes, or, in short, those requiring a high 
 percentage of Mg, Al, Fe, as well as silica. The fact that 
 the limestone in the present instance is over 96 5 per cent 
 pure calcium carbonate would seem to be sufficient reason 
 for the absence of secondary minerals. This being so, it 
 might naturally be expected that the only effect of the 
 igneous eruption would be the dissolving of part of the 
 limestone by the trap. Such, indeed, seems to be the case, 
 for on each side of the dike occur six to eight inches of a 
 greenish rock, lighter in color and finer grained than the 
 trap. A partial analysis of this rock showed the presence 
 of 16 per cent of lime, carbon dioxide being absent. The 
 trap proper contains 9 per cent, as the following analysis 
 shows. A mean of several analyses gave the following 
 .result : 
 
 TRAP FROM STONY BROOK. 
 
 SiO 2 . , ... .- . . . . . : ; . . 46.78 
 
 TiO 2 . . . : , . . . . u . J .. . 0.99 
 
 CaO . . . . ....... . . . 9.1 1 
 
 MgO . . . . , . . . . . , i, . 7.38 
 
 Na 2 O . . . . --.-. ...> . ... . .. -.- . 5.10 
 
 K 2 ........ ,,/ . ... , . 052 
 
 Li 2 O . . trace 
 
 A1 2 3 . , . . 19-28 
 
 Ft- 2 O 3 , 6.1 1 
 
 FeO 4.16 
 
 CoO trace 
 
 MnO trace 
 
 H 2 O.no , 0.05 
 
 HO -- 110 0.06 
 
19 
 
 BaO none. 
 
 SrO . . % " 
 
 CO 2 
 
 P 2 O 6 . not test. 
 
 S . trace. 
 
 99-54 
 
 In regard to the presence of the oxide of cobalt a word 
 of explanation is perhaps needed. 
 
 In almost all the analyses when the magnesium ammo- 
 nium phosphate precipitate was dissolved off the filter and 
 evaporated in nitric acid, a rose red color was noticed 
 towards the end of the evaporation. Some of this, very 
 likely, was due to manganese, but the bead test seemed to 
 indicate the presence of very minute quantities of cobalt. 
 It was hoped that by taking large amounts of the rock 
 more certain evidence of the presence of this element would 
 be found. Such was not the case, however. Proof of the 
 presence of cobalt or nickel in appreciable amount in these 
 rocks would be of considerable interest. At present it is a 
 subject for further investigation. The sulphur present is 
 probably all there as pyrites, since a few specks of that 
 mineral were observed in the rocks. 
 
 The ferrous iron was determined by decomposition with 
 sulpnuric acid in sealed tubes. 
 
 The description of the trap is here appended. 
 
 MICROSCOPIC CHARACTER OF THE TRAP. 
 
 The trap at Enterprise, near the lower end of the dike, has 
 the ophitic structure of diabase. (See plate, Fig. 5.) The 
 base is entirely granular and shows many places clouded 
 with inclusions. The feldspar, which appears to be labra- 
 dorite, extinction angle=i83o' to I93(/, has altered in 
 part, forming the usual decomposition products. Pale 
 
20 
 
 brown angite occurs mostly in grains; also in long columns. 
 No crystal outlines were noticed. The pyroxene has begun 
 to pass to a diallage structure, though not to the extent 
 that is shown in the rock at Stony Brook. Considerable 
 magnetite is present, and hornblende occurs, apparently as 
 an alteration. 
 
 At the exposure at Stony Brook the rock is in general 
 the same. It is finer grained and has suffered more 
 decomposition. There is much decomposed feldspar and 
 the field is cloudy. 1 he base is granular. The feldspar is 
 apparently labradorite, while the pyroxene has much diallage 
 structure. Hornblende is rather common and in some places 
 are veins of secondary hornblende intergrown with microlitic 
 feldspar and magnetite. (See plate, Fig. 6.) Towards the 
 outer edges of the dike the pyroxene is almost all ortho- 
 phombic. When thin sections are examined in reflected 
 light the crystals show the schiller effect of bastite. Run- 
 ning up and down through the trap are several veins of de- 
 composed material consisting of hornblende and completely 
 saussuritized feldspar. 
 
 THE DIKE AT YORK HAVEN. 
 
 This dike, which is notable on account of its size and 
 extent, is located just above the station of York Haven, on 
 the Northern Central Railroad, on the Susquehanna River. 
 
 It is well displayed by the cut of the railroad and in a 
 quarry formerly operated here. 
 
 It extends across the river into Lancaster county and is 
 exposed in the same manner there as on the York county 
 side. 
 
 la the river are numerous boulders of the rock, which in 
 times of low water almost fill up the channel. 
 
 The width of the trap cannot be ascertained with any 
 degree of certainty, since the contact of the dike and 'the 
 
21 
 
 adjacent rock is concealed on each side. It is exposed 
 for over two hundred feet in its natural position, beginning 
 at the lower part. Along the river it makes an elevation, 
 of a hundred feet or more ; back in the country this is lost 
 in a general range of hills, and its presence is known only 
 by means of surface t>oulders. The trap occurs in compact 
 masses, is rather easily worked for building purposes, and 
 formerly commanded a ready sale in York, Baltimore and 
 other cities. 
 
 In regard to the intrusive or extrusive nature of the trap 
 the evidence is not very satisfactory. On the upper side 
 the first sedimentary rock seen is evidently not in contact 
 with the trap and has not suffered any metamorphism due 
 to the presence of an igneous eruption. On the lower 
 side the contact is not sharply exposed. As nearly as can 
 be seen, however, the trap does not lie conformably on the 
 sedimentary rocks below, but appears to break across the 
 beds. These lower beds have suffered undoubted meta- 
 morphism. 
 
 The texture of the rock is rather dense wherever ex- 
 posed. In passing from the lower part to the upper, an 
 increase in the size of the grains is noticed, accompanied by 
 a change in the character of the rock. This will be brought 
 out more fully in the remarks under the microscopic 
 character of the trap. 
 
 Towards the middle of the dike a columnar structure like 
 that in basalt is noticeable. At the lower edge the trap 
 has broken into thin layers, presenting the appearance of 
 upturned beds of sedimentary rock. 
 
 The above observations tend to an intrusive rather than 
 an extrusive origin. 
 
 MICROSCOPIC CHARACTERS. 
 
 It was stated that the trap at the lower side is fine in 
 grain. The rock consists of plagioclasc feldspar, augite, 
 
22 
 
 dark brown mica, hornblende and titaniferous iron. The 
 feldspar is labradorite. Colorless augite occurs in 
 both grains and the irregular columnar patches like those 
 in diabase rocks. The greater part of the augite, however, 
 is in well formed crystals showing the usual cross 
 cleavage. 
 
 This gives to the rock a pronounced basaltic appearance. 
 (See plate, Fig. 3.) 
 
 Dark brown mica is rather common in scales ; no crystal 
 faces are shown. In some places along the edges and 
 between the crystals of augite occur patches of hornblende. 
 
 The base is fine granular and in m my places is clouded 
 with inclusions and microlites, replacing almost entirely 
 the pyroxene. Very small, colorless needles, visible with 
 the higher powers, occur in places. They are possibly 
 apatite. 
 
 This rock is evidently a dolerite. 
 
 The greater part of the trap here, however, consists of 
 the coarse grained type with a gabbro structure. (See plate, 
 
 Fig. 4-) 
 
 The feldspar has a high angle of extinction, varying from 
 24 to 32. This is rather high for labradorite. It may, 
 perhaps, belong to one of the mixtures between labradorite 
 and anorthite. The high percentage of CaO and rather 
 low percentage of Na 2 O (see analysis) indicates an approach 
 to the anorthite molecule. 
 
 The pyroxene has passed almost entirely to the diallage 
 structure. No augite crystals were noticed. Mica and 
 hornblende are present, and inclosures of titanic iron 
 common. 
 
 The feldspar has begun in some places to show the hazy 
 appearance due to decomposition and formation of saus- 
 surite. 
 
 The following is an average analysis of the trap from 
 near the middle of the dike : 
 
23 
 
 ANALYSIS OF TRAP FROM YORK HAVEN. 
 
 SiO 2 45.82 
 
 TiO 2 6.07 
 
 A1 2 3 1770 
 
 Fe 2 O 3 2.11 
 
 FeO 6.15 
 
 MnO trace. 
 
 CoO trace. 
 
 CaO 13.00 
 
 MgO 6.66 
 
 BaO | 
 
 SrO .} none - 
 
 K 2 O 0.82 
 
 Na 2 O 2.42 
 
 Li 2 O trace. 
 
 Cr 9 O, ) 
 
 ,* 
 
 J 
 
 not tested for. 
 
 100.75 
 
 On the presence of cobalt oxide, see the remarks under 
 the analysis of the Stony Brook dike. 
 
 A feature of the trap is the large number of veins of 
 augitic material which run for long distances in all 
 directions through the rock. Sometimes long needles of 
 zeolites are intergrown with the altered veins. 
 
 In the more altered parts of the trap occur veins of 
 secondary minerals, forming whitish masses, in which are 
 long, needle-like zeolites, quartz and small, perfectly formed 
 sphenes. Lustrous plates of bronzy pyroxene are not 
 uncommon. 
 
 Biotite occurs in plates a quarter inch in size. 
 
 On the exposed surfaces of the rock occur immense 
 numbers of small chabazite crystals, and also considerable 
 stilbite. Analyses of these minerals have been published. 1 
 
 i C. H. Ehrenfeld, Jour. An. and App. Chem., vol. 6 (2) ; vol. VII (i). 
 
24 
 
 GENERAL SUMMARY OF RESULTS.' 
 
 Of the section measured in the Trias up to York Haven, 
 the lower part probably represents the Norristown of 
 Lyman. 
 
 In the upper part the presence of plant fossils character- 
 istic of the coal fields of Virginia marks a connection 
 between these beds and those of the South. 
 
 This part of the formation probably corresponds to the 
 lower portion of the Gwynedd of Lyman. 
 
 The traps consist of dolerite, gabbro and diabase. 
 
 At York Haven the original magma was basaltic. 
 
 The lower part of the dike still has a basaltic structure, 
 while the middle and upper portions have become coarse 
 grained with a gabbro structure. 
 
 The Stony Brook dike is a diabase. It has suffered 
 considerable change and has developed a large amount of 
 orthorhombic pyroxene. 
 
 ACKNOWLEDGMENT. 
 
 This work was carried out under the direction of Pro- 
 fessor Amos P. Brown, and I would express to him my 
 most sincere thanks for the interest he has taken in the 
 work and for the valuable instruction received from him. 
 
 To Professor Edgar F. Smith I wish to extend my 
 grateful thanks, not only for the instruction received from 
 him, but for his kindness to me as a friend. 
 
 ADDENDA. 
 
 At bottom of plate, line six, read vein for view. 
 
 The figures all show magnification of 35 diameters, 
 and except Fig. 2, were taken between x nicols. 
 
1. Metamorphosed shale with apatite, York Haven. 
 
 2. Slate showing aggregates of magnetite, York Haven. 
 
 3. Dolerite from York Haven. 
 
 4. Gabbro from York Haven. 
 
 5. Diabase from Enterprise. 
 
 6. View of Hornblende in diabase, Stony Brook. 
 
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