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Pa, Tlic Area specially studied Description of the I'innacle Hills Relationship to tlie surroiindiny Country Altitudes in Rocliester and its Vicinity Eskers in I'ittsfcjrd Relationship to Druinlins and Terminal Moraines on the Relationship to (Hacial Movements Probable Orijjin of these Eskers Application of this Explanation to Eskers elsewhere , H. iSi 182 I {7 1S8 )Uth. 'I"HE Area specially studied. On the southeastern border of Rochester, X. Y., a remarkable esker series, named the I'innacle hills, extends nearly four miles from east-northeast to west-southwest, rising from an approximately level country and forming the only conspicuous elevations of land close to that city. Under the guidance of Mr. (r. K. Gilbert, this esker was examined by most of the geologists who attended the meetings of the Geological Society of America and of Section E of the American Association for the Advancement of Science in Roch- ester last August, and on the following morning about an hour was •This paper was ori^'inally prepared lor and read at the (ittawa meeting of the Cieolugiiai Society of America, December ., , li.j I82 !<()( HKSTKR .\( AI>I.MV OC SCIF.NCE. [Jan. 9, given to discussion of the manner of its formation through the agency of the ice-sheet and the streams produced l)y its melting. liefore stating some of the opinions brought out in that discussion, and attempting a full incpiiry concerning the processes of accumulation of this and other eskers and kames, we will first go again, as I did on following days, over the Pinnacle hills and describe their contour and numerous sections exposed by excavations for road material and for the passage of streets. The other drift deposits and contour of their vicinity will be noted, and a second series of eskers Iving .several miles farther southeast in Pittsford, which I also examined, will be described, with their relationship to prominent drumlins near, and to terminal moraines more remote, on the south. Descrii'iion (II niK Pinx.xci.k Hills. From lirighton village and station on the New ^'ork Central rail- road, thrc. miles southeast from the .station in Rochester, this promi- nent range of hills extends in an almost straight course about four and a half miles west-southwesterly to the (lenesee river close south of the State dam. In passing the east end of this e^ker, the Erie canal turns from a due east to a due south course. Along its first mile from lirighton the esker rises 75 to 150 feet above the country on each side, and declines in height from 125 to 75 feet near the western end of this portion, where it is known as Cobb's hill. Imme- diately to the west, near the residence of Mrs. \V. H. Cobb, a sag in the esker, as it was originally, before being cut down for the extension of Monroe avenue, had a heigiit of only about 50 feet. Next west- ward the esker rises in the distance of a hall mile to its highest point, called the Pinnacle, 200 feet above the nearly plain region on the north and sjuth. Thence the continuation of the esker along its next two miles, varying in altitude mainly from 150 to 100 feet above the general level, is occupied, in order from ea^t to west, by the St. Patrick Cemetery, the Highland Park, which includes the Mt. Hoi)e reservoir in its western part, and the extensive Mt. Hope Cemetery In its next mile west to the river, the ridge is lower, having a height uf only 80 to 50 feet above the State dam. The northeastern end of this hill range at Prighton is very definite, overlooking a wide expanse of the low land ; but its western end is indefinite, for in the line of its continuation west of the (Jenesee it is represented along a distance of at least two miles (which is as far as my examination extended) by a low ridge, mostly 30 to 40 feet ab(;ve the general level. Petween • •••>•«* •» ♦ • • . •• • /• •• • • • • • •#'• ••#••,••••, ««93-] UHHAM — ESKERS NEAR ROCHESTER, N. Y. 183 the Mount Hope Cemetery and the (lenesee river and farther to the west, the material of the ridge is 'argely till, which shows that low portion to be a marginal or interlobate moraine ; but the high range of the Pmnacle hills from Brighton to the Mt. Hope Cemetery i.s clearly an esker, 3/, miles long, consisting of interbedded gravel and sand, here and there enclosing boulders, sometimes in surprisintr abundance, but containing no till in the extensive sections nor on its surface. The width of this hill range is mostly about a sixth of a mile but vanes from a tenth to a half of a mile. Along its whole extend It IS a smgle range, nowhere presenting a combination of parallel series of hdls ; but, in some parts, especially in the Highland Park and near the reservoir, it is incised on each side by ravines between spurs and outlying hillocks of the main belt, and its top is occasion^ ally very uneven in contour, with infrequent bowl-shaped hollows lo- to 50 feet below the surrounding surface. The profile of its crest line undulates in an irregular way, generally varying 50 to 100 feet in height upon each mile or half mile ; and it nowhere maintains a level course for any considerable distance. In the vicinity of the Pinnacle and :n many other places, the slopes on each side are very steep ranging to a maximum of about 30 degrees ; and the crest line has occasional slopes of half this steepness. More commonly, however the slopes vary from 6 to 15 degrees, having from 10 to 2s feet of ascent in a distance of 100 feet. When my first contribution to geology was published, sixteen years ago, " On the origin of Kames or Eskers in New Hamp- shire, • (■) these classes of the modified drift, produced jointly by the ice-sheet and the water of its melting, had not been discriminated from each other. Every knoll, hillock or hill, short or long ridge or series or network of ridges composed of irregularly and often aiui- clmally bedded gravel and sand, retaining nearly the original form in which It was accumulated, was then called interchangeably a kame esker, or as, or a series of /cames, eskers, or asar. The first of these terms is of Scottish, the second of Irish, and the third of Scandina- vian origin, the last being Anglicized to ^.ar, with .w. as its pluril form. It is found very desirable, however, to subdivide these gravel and sand accumulations into two classes, as proposed by McGee n and Cha mberlin, (') giving to the hillocks and short ridges the name {. ) Proc. A. A AS., Vol. .XXV, for ,87^ pp. =,fi-.2, I.S4 KOt IIKSI KU A( ADIMV OK SCIKNl.K. [Jan. 9, /ciiiiia, while the prolonged ridges are termed /'.vXr/.v or osars, exceiiting tlicir neciiliar development in northeastern Iowa, where they are com- posed chietly of loess or fine silt and have received the name /(///r/, alike whether singular or jjliiral. (') Kanu-s, as thus detined, usually or often constitute an imi)ortafl part of the terminal moraines, and they are also frecpient on many other jjortions of our drift sheet. Kskers are found likewise both in the vicinity of terminal moraines, some- times being evidently of closely contemporaneous origin, and also remote from moraine belts. In length the eskers or osars vary from a mile or less to several miles, and in Maine and Sweden they extend in many continuous series, 20, 50, and even 100 miles or more. Their courses are commonly somewhat crcjoked, like those of rivers, but in general they run in parallelism with the glacial stria; and directions in which the ice-sheet moved ami carried its boulders and other drift. The structure of the Tinnacle hills esker is well exhibited near its northeast end, near Monroe avenue, and at various places separa- ted only by short intervals, thence westward to Mt. Hope avenue and cemetery, by excavations for the use of its gravel and sand in road- making and masonry. Less than a quarter of a mile south of iirighton, a cut on the northern slope of the east end of the esker, just east of the north to south road (.\rbutus avenue), has a depth of about 30 feet and length of some 12 rods. The upper 10 feet are fine gravel and sand, almost levelly bedded, beneath which the remain- der of the section consists of very coarse but distinctly stratified gravel, with a nearly uniform dip of 15" W. S. \V. 'i'liis coarse gravel contains cobbles and rock fragments of all sizes, up to ij^ feet in length, packed closely together, their interstices bei ig fdled with liner gravel, sand, and very line silt. About two thirds of all the stones art' much water-worn, so as to have rounded forms ; nearly all of the remaining third are somewhat worn, being subangular ; and only about a twentieth part are rather sharply angular, with little or no evidence of attrition in their transportation by the glacial river. ]''ully half of the small gravel, up to six inches in diameter, are Medina sandstone ; and about a third of the cobbles and masses from 6 to 18 inches in diameter are Archivan gneissoid rocks. Only four bould- ers of larger size, none of these exceeding four feet in diameter, were seen in this section. Close west of this road, nearly opposite to the foregoing and at a distance of 10 to 30 rods southwest from it, a larger excavatit)n. *'•'. ^y -' .^'K^'S*-'- ',' ''"^ I'lL'istcKcne Historvof in.rthciistcrn Inwa," in llic Kltven'.li .Amuia Kcport (il tlic L . S. (itcil. Survey, fur iSSy->ji.). '«93.] iri'HAM— KSKF.RS NKAR KOCHKSTKK, N. V. '85 also in the northern side of the esker. consists almost wholly of fine jrravel and sand, with stratification mostly inclined 5" to 20" south- ward. This section, 30 to 40 feet deep, and the surface of the esker immediately adjoining it, have only very rare boulders ; but within a short distance the southern slope of the ridge, where it is cut for the road, has many boulders on the surface and in the uuper 10 feet of the k'ravel and sand. The rather broadly rounded toj) of th^ ^sker is here about So feet above the general level on the north, east and south. In its central part, .-5 feet below the top and some 20 rods from its northern ba.se, a small space of this section, 10 feet long and 6 feet in height, shows three sharp faults, each having 2 to 3 feet of displacement, with overthrust from south to north. The beds overlying the faulted portion, which was near the bottom of the e.vcavation, and the con- tinuations of the faulted layers away from this place on each side, were undisturbed, dipping 10" to 15" S. or S. S. W. Fifteen to 40 teet east from these faults, slightly higher beds show eight repetitions, within a thickness of 8 feet, of layers of gray gravel, 3 to 12 inches thick, separated by layers of fine yellow sand . to 3 inches thick, 'I'hese alternations probably represent the rapid and strong currents of a glacial river during the fast melting of the ice surface by day and the slow currents at night, when ablation was at its minimum or ceased. Another large excavation 300 to 500 feet we.st of the last, like- wise in the northern side of the esker, has a vertical face of 40 to 50 feet, consisting of intcrbedded gravel and sand in its upper half, while its lower half is mostly sand. 'I'he largest cobbles in the gravel are about one foot in diameter, and no boulders were observed. Mainly the dip is 10" to 20" southward, but at the east end of this section it's upper 10 to 15 feet are much contorted, with a prevailing northerly dip of 10" to 15". Jn the southeastern side of the esker, opposite to Mr.s. \V. H. Cobb's house, an excavation about 25 rods long and 50 to 60 feet high consists in its upper part, to a depth of 6^0 20 feet from the surface along its whole extent, of sand and very coarse gravel enclos- mg exceedingly abundant boulders of all sizes up to 6 or S feet in diameter, far more plentiful than in the ordinarv till of this region. 15elow this portion, the remainder of the section, extending downward 30 to 40 feet, is irregularly interstratified gravel and sand, with only infiajuent boulders. The whole section shows stratification by cur- reiiLs of water, and according to my estimate nineteen twentieths of i86 KoiUKSIKK ACADK.MV OP SCIKN( K. I Jail. 9. the gravel and small rock fragments are rouiuled or at least mucii worn on their edges and corners. Other sections which were examined in our excursion on the northern slope of the esker near this place and about a quarter of a mile to the northeast, show the same astonishing profusion of boul- ders with the upjier coarse gravel, underlain by beds having fewer boulders. The gravel and sand are characterized by irregular and often oblicpie bedding, variable thickness of individual layers, and occasional oblique or nearly vertical faults with small amount of dis- placement ('). Boulders are also strown in considerable numbers on the surface of this part of the esker, but elsewhere along most of its extent they are usually rare both on the surface and in excavations. Mr. (lilbert called attention to the origin of the boulders, and pointed out the very significant fact that many of them are of the Niagara limestone, which can have been transported no moie than three or four miles from its parent ledges, since the northern limit of this formation lies within that distance. Some of these boulders were seen on or near the Pinnacle, at least ^oo feet above the outcrops on the plain country northeastward from which they must have been derived. Continuing over the Pinnacle and through the Highland Park, I examined numerous sections, all of which were interbedded gravel and sand vyith only very rare boulders or more commonly none. Occa- sionally, however, a boulder 5 or even 10 feet in diameter is found on the surface, or in a section, remarkably in contrast with the water- deposited sand and gravel, in which the largest pebbles and cobbles range from a few inches to a foot, or seldom one and a half feet in diameter. l-'rom the Pinnacle to the Mount Hope cemetery, most of the excavations are chiefly sand. The cut made west of this cemetery by a branch of the New York, Lake Erie & Western railroad has a length of nearly a quarter of a mile from north to south and is from 15 to 25 feet deep. Large portions of this section are true till, or clay, sand, and small and large rock fragments, mingled in an unstratified deposit ; but, like the till of the surrounding country, it contains only few large boulders. Among the half dozen boulders of greater size than two feet in length seen in the eastern face of this excavation, oae of the largest, about five feet in diameter, was Niagara limestone. With the depos- (i.) Numbers 323, 324 and 325 of the list of photographs of the Geological Society of America (Bulletin, G. S. A., Voi. Ill, p. 472* are views of sections of the Pinnacle hills esker at this locality, photographed and piescnled by Professor H. L. Fairchild. »893.I UI'HA.M — KSKEkS NEAR RUCUESTER, N. V. 187 its of till are many intercalated layers of stratified sand, from i to 5 feet in thickness, often continuous along a distance of 100 feet or more. These lay ;s are mostly horizontal or only slightly inclined, and no contortion nor evidence of erosion or tumultuous pushing for- ward was observed. Beyond its intersection by the Genesee river, this ridge is the rite of the Rapids Cemetery, and thence it extends nearly due west two miles along or close to Hrooks avenue. It rises by usually gentle slopes ,?o to 40 feet above the land on its south and north sides, and has a width of 25 to 50 rods, being often quite irregular in contour, whirh with its clayey soil and occasional boulders, gives it a morainic aspect. Where it is cut by the Hulfalo, Rochester ^: I'ittsburgh lail- road, nearly two miles west of the river and between an eighth and a third of a mile north of Hrooks avenue, several recent excavations si Nved about half of its material to be till, and the remainder very compact stratified sand. These unlike deposits are irregularly accu- mulated together, but no interblending was seen. The till has no marks of water action, and the sand is free from boulders or gravel, and is horizontally bedded or nearly so, being sometimes 5 to 15 feet thick with an exposed extent of fully 100 feet. Rt'latioHship to the surrouihiin;^ 6^tf//«/;j'.— Throughout the city of Rochester, excepting the Pinnacle hills and the gorge of the Genesee below its falls, the surface is nearly a plain, with slight descent toward I-ake Ontario. The underlying Niagara and Clinton formations are covered generally with only 10 to 20 feet of drift, which is mainly Lill and in small tracts stratified clay or sand and fine gravel. North- ward from Rochester, the surface in Irondequoit and Greece town- hips declines with a gradual slope 200 to 250 feet in the distance of 5 to 7 miles to Lake Ontario. The fjord-like Irondequoit bay, lying between Irondequoit town- ship on the west and Webster and Penfield on the east, stretches about '(w^ miles southward from Lake Ontario, with a width varying from one m.le to a half mile, bordered by clil't's 100 to 200 feet high, which rise to the general plain on each side. The maximum depth of Iron- de(iuoit bay is 80 feet, which must be added to the height of the bluffs to give the total depth of the eroded valley ; and its southern end, where the Irondequoit river flows into it, is about five miles east from the center of Rochester. Before the Ice age the Genesee doubtless enteied the lake through this valley, probably leaving its present course near the mouth of the Honeoye creek, flowing eastward, through Bush township and the southern part of Mendon, and thence northward along the Irondequoit river and bay. In the southeast I iSS ROCHESTER ACADK.MV OK SCIK.NCE. [Jan. 9. edge of I'ittbford tlie Irondeiiuoit, where it is crossed by the Erie canal and for three miles southward, is about loo feet lower than the Genesee near the south line of the city of Rochester, above the State dam. Rspecially thick accumulations of the glacial drift in Memlon caused the (lenesce after the Ice age to take its new course through Rochester ; and its rock gorge, extending from the center of this city to its mouth at Charlotte, has been eroded during the Postglacial or Recent ei)och, of which, like the gorges below the falls of Niagara and of St. Anthony, it affords a means of measurement, if the e.xtent of recession of the Genesee falls during the present century can be determin 'd. Southward and eastward, elevations of equal height with the I'innacle hills are first found at the distance of 7 to 10 miles, being prominent drift accumulations later to be described in this paper, lying in the southwest part of I'ittsford ^ id northwestern Mendon. and between Victor and Kairport. 'l"he 1 elation of the Pinnacle i.llls to the adjoining region will be further exhibited by the following list of altitudes, which are mostly derived from maps in the oflice of Mr. J. V. McClintock, city engineer of Rochester, others being from the tJnited States Lake Survey. They all are referred to mean tide sea level. Altitudes in Rocliestcr and its I'icinity. 1 Lake Ontario, low and high water, 2\^-2^,^) ; ordinary stage. . Irotjuois beach, between Irondecjuoit bay and the Genesee river (Gilbert) Erie canal, coping and tow-[)ath of viaduct crossing the Cicn- esee river in Rochester, 510; water _. New York Central railroad track at Rochester station Wide Waters of the Erie canal on southeastern line of Roch- ester Railroad at Brighton station . _ Can J , at Brighton Summit of Arbutus avenue one-fourth mile south of Brighton, crossing the east end of the I'innacle hills esker Top of esker about 50 rods west of last Top of esker one third mile farther west Depression close southwest of last Highest point of Cobb's hill, one-third mile farther W. S. \V.. Top of esker about 40 rods westward the Sf;i. 436 508 5>6 500 460 4S0 570 652 59° 663 60S ^^J3\ Ul'HAM — KSKliRS NKAK kOCHESTKR, N. Y. Feet IntL'.-sectioii of ^[()nroe and Highland avenues, at Mrs. W. H. Cobb's residence, immediately soutii of last The Pinnacle, one-half mile farther west Summit of Pinnacle avenue, crossing the esker one-third mile farther west Top of esker in Highland park, at the Memorial Pavilion... Mt. Hope reservoir, water surface Summit of South avenue Summit of Mt. Hope avenue. Highest portions of the esker in .Mt. Hope cemetery, about. Crest of morainic ridge extending westward as a continuation of the Pinnacle hills, where it is cut by the Cenesee Val- ley branch of the New York, Lake Erie & Western rail- road Same, on east bank of the Centsee river Same, west of the river, at the Rapids cemetery and onward.. 555- (ienesee river above the State dam, near the foregoing At foot of this dam At the Clarissa street bridge At the Court street bridge At the Andrews street bridge Upper falls, toj) of rock, 476 ; water in ordinary stage at brink and foot of the full ,,, ■ '" " - t/o' Above and below the Middle falls -,■,,. At mouth of Deep Hollow creek and brink of Lower falls At foot of Lower falls . At the steamboat landing, about one mile north of the last, on the level of lake Ontario Seneca Park bridge, spanning the gorge close below the Lower falls Highest ground at the Rochester University Canal and railroad at Pittsford, about Irondequoil river under the viaduct of the Erie canal, about Turk's hill, a station of the U. S. Lake Survey triangulation, near the south line of Perinton township, about 12 miles southeast from the Pinnacle hills Rush reservoir of the Rochester Water Works, 9 miles south of the Mt. Hope reservoir Hemlock lake (ma.ximum deinli, 87 feet), source of the Roch- ester water supply, 19 miles from tb - Rush reservoir 189 above sea. 544 749 5S3 650 634 r,,7 622 675 583 559 -560 508 504 50- 493 484 -3-^7 -34'^ 345 ^5' 247 460 520 4O0 400 928 753 S98 IQO ROCHESTER ACADEMY OK SCIENCE. [Jan. 9, ESKERS IN PiTTSFORU. From 2i^ to 3 miles southeast of Brighton, the New York Central railroad makes a long cut through the northern end of a second esker series, which takes a course approximately at right angles with that of the Pinnacle hills. Beginning close south of Allen's creek, in the southwest corner of Penfield township, this belt of kames and eskers runs south-southeasterly through the east half of Pittsford and about a mile into the southwestern corner of Perinton, terminating in a sand l^lateau, which abuts upon the western base of the prominent Turk's hill range of drumloid drift. The length of this Pittsford esker series is about seven miles. In its northern third, extending from Allen's creek southward to about a mile east of Pittsford village, the width of this belt varies mainly from a half mile to fully one mile, and it consists of a princi- pal broad north to south esker ridge, becoming narrower and inter- rupted southward, with a considerable lateral expansion, especially on the east, in kames, or short ridges, mounds and hillocks, all being composed of sand and gravel, with infrequent enclosed boulders. I'he cut for the railroad is about a half mile long and 50 feet deep. Its greater part is yellow sand, nearly horizontal in stratification, except- ing at the margins, where the bedding is more irregular, prevailingly dipping downward like the surface slopes. In this sand are occa- sional thin gravelly layers, but these are nowhere conspicuous. Very rare embedded boulders were seen. Only two, which were respect- ively about 3 and 5 feet in diameter, were exposed in the section at the time of my visit, and scarcely a half dozen in total lie at the foot of the banks on both sides of the railroad. The basal part of this section, however, for about an eighth of a mile west from its center, consists of coarse gray gravel, containing very closely packed gravel stones and cobbles up to 6 or 8 inches in diameter, but no larger boulders. On the north side of the excavation the gravel reaches to a height of about 20 feet above the track, and displays a very distinct anticlinal stratification. About i>^ miles southeast from this ra-'road cut, a small excava- tion for the passage of a north to south road through a kame deposit, chiefly of sand, near the east line of Pittsford and the east border of the esker and kame belt, reveals a boulder 3^^ feet in diameter, embedded 10 feet below the surface. Beneath and above the boulder, the stratification of the sand and gravel is contorted and curved, in conformability with the outline of the rock mass. i893] UPHAM— ESKERS NEAR ROCHESTER, N. Y. 191 After an interruption or gap about 40 rods in length, the more southern portion of the series, from a point about a mile east-south- east of Pittsford village to its termination about a mile southeast and sou.n of the village of Bushnell's Basin in Perinton, is well described as follows, by Mr. Charles R. Dryer, in a paper which also treats of the Pinnacle hills. Irondequoit bay, and the massive hill ranges of till south of Pittsford and Fairport ('). Mr. Dryer, following the early usage of the term kaine, applies it to the narrow esker ridge, with steep slopes and sharp crest, which he describes one to three miles south- east of Pittsford, succeeded in the next mile or more by a sand plain or plateau. " The north end is a sharp ridge of very coarse gravel, fifty feet in height, one mile long, and in shape like a rude fish-hook. It is separated from^he southern portion by the channel of Irondec|uoit river, which has cut the kame completely in two. In the southern portion the gravel is overlaid by fifty feet of fine sand which spreads out toward the southeast in a sheet a mile or more m width. This kame forms a dam across the valley, complete except for an interval of less than one-fourth of a mile on its western side. The Erie canal avails Itself of this kame to cross the valley and by a fifty-foot embankment restores what probably once existed as a natural feature. South of the kame the valley is as level as a floor for three miles up the stream and was evidently once the site of a lake whose waters were held back by the kame as a dam." Relationship to Drumlins and Terminal Moraines on the soi//h.—To understand the history of the recession of the ice-sheet in this region and of the accumulation of its drift, it is needful for us to take for a moment a somewhat broad viev southward. Beginning within a half mile south of Pittsford, drumlins are admirably developed upon an area extend- ing six or seven miles to the south, into the northwest part of Mendon. They also form the crests of a massive drift ridge which stretches from Fairport south to Victor, culminating in Turk's hill ; and beyond a depression, through which the railroad from Rochester to Canandaigua passes, similar massive, drumlin-crowned highlands extend from Victor several miles to the south and southwest. These highlands appear to me referable to the class of drumlins, rather than to that of terminal moraines marking the outlines of the ice-front at any stage of temporary halt in its general retreat. Eastward from this region, drumlins occur in extraordinary abundance for a distance of 60 miles, to the vicinity of Syracuse ('). wi,h*'nap'!'A^,ri:,''8^'. ^'"'°^'' °^ ''"' I'""'"-'""" R'^S-"- Am. Gcolo^nst, Vol. V, pp. .0.-.07, V /V' oJ'- '"''"T!?' "7'"= Parallel Hills of Western New York," Trans N V Acad of Sri \ol. , .88., pp. ,8-So; Annals, d,.., Vol. H, pp. 24^-^66, with map. ' ^■^■^^'''^- of Sci., y^A^lAx:'^':^^^^^':^.'^'''''''^'''^''^'' '^*-'«'-" '"■ -^■•-■"- Vork,"Am. Jour., Sci., III. 362, De",''"?S !'''"'"" '^""''''■''"''''^ Accumulation of Drumlins." Am. Geologist, Vol. X, pp. 33^- 192 ROCHESTER ACADKMV OK SCIENCE. [Jan. 9, Between 35 and 60 miles smith of Rochester, conspicuous termi- nal moraines run approximately from west to east, as described and mapped by Professor T. C. Chambcrlin ('). On the meridian of Rochester these moraines are somewhat interblended, fragmentary, and irregular in their development upon a width of nearly 25 miles from the southern ends of Conesus and Hemlock lakes southward lo the vicinity of Hornellsville. Farther to the east, for a distance of about 150 miles, to the Catskill mountains and the Mohawk river, they are more distinctly developed as two morainic belts, of which the southern one is traced in a slowly curving course, convex toward the south, along the valleys of the Canisteo, Tioga and upper Susque- hanna rivers, while thr northern one passes in a more sharply curved and lobate course by the south ends of the Finger lakes to Ilion and Herkimer on the Mohawk. In the valleys extending southward from the heads of the larger Finger lakes the thickness of the northern moraine a[)pears to be several hundreds of feet, and in the case of Seneca lake perhaps inore than 1,000 feet ; but on the intervening plateaus the thickness of the morainic drift is comparatively insig- nificant, averaging probably no more than 25 to 50 feet upon widths varying from one to two or three miles. A more distant moraine, however, lying on and near the bound- ary of the glacial drift, extends from the vicinity of Salamanca, N. Y., east-southeasterly to the Delaware river at Belvidere, N. J., and to Staten Island, the Narrows, and Long Island. This moraine, described in Pennsylvania by Professors Lewis and Wright, (-) passes about 100 miles south of Rochester. Relationship to Glacial Movonents. — The currents of the ice-sheet flowed perpendicularly toward its boundaries and marginal moraines, that is, to the south or somewhat west south for the region about Rochester and Pittsford ; but during the recession of the ice from that area, its currents were in some portions deflected much to the west, because of more rapid melting of the ice on that side and con- sequent indentations or embayments in its border. This faster melt- ing on the west was probably at first due in large part to the laving action of the glacial Lake Warren, which extended from the western part of the basin of Lake Ontario over the upi)er Laurentian lakes, outflowing at Chicago to the Des Plaines, Illinois, and Mississippi rivers ; and in the later stage of the glacial recession when the Roch- M.i riiird Annual Report of the U.S. duol. Survey, fur 1S81-S2, pp. ^551-^60, with Plate XXXIII. U'.l Report Z, Second Geol. Survey of Pennsylvania. 1 893- J Ul'HANr — ESKERS NEAR ROCHESTER, N. Y. 193. ester and Pittsford eskers were formed, the ice-melting was likewise promoted by the incipient Lake Iroquois, outflowing by Rome to the Mohawk and Hudson. According to notations of glacial striiij by Chamberlin, Gilbert, and Dryer, their courses are as follows : near the northeast corner of the city of Rochester, S. S. W. to S. W. ; near the southwestern bound- ary of this city, S. W. to W. S. W.; and in (Ireece, the next township northwest of Rochester, four courses, intersecting or on contiguous rock exposures, S. S. E., S. S. W,, S. W., and W. Thesouthward courses are doubtless somewhat earlier than those running to the south- west and west, which belong to the short time when the glacial cur- rents were deflected during the departure of the ice. Upon all the region of the Finger lakes the glacial striation is approximately from north to south, in parallelism with these lakes and the intervening ridges and plateaus. On the north the grand ice currents over the ^'rovince of Ontario moved mainly southward, with convergence from the southern part of (Georgian l^ay southeasterly, and from Mon- treal and the upper St. Lawrence southwesterly, toward the basin of Lake Ontario and the great re-entrant angle of the glacial border at Salamanca in southwestern New York. The trends of eskers and drumlins testify of the directions of the currents of the ice-sheet as trustworthily as the courses of glacial striation on the bed-rocks, with which the esker and drumlin ridges are parallel. Eoth these classes of drift accumulations, however, were formed near the border of the ice during its recession at the close of the (llacial period ; and they consequently often record local deflec- tions of the glacial currents caused by unequal rates of melting and the resultant sinuosities of the ice-front. The IMttsford esker series, trentling south-southeast, is nearly parallel with the general move- ment of the ice-sheet, both during the time of its maximum extent and thickness and during the decadence ; but the Pinnacle hills, trend- ing west- southwest, show that a considerable local indentation or embayment in the waning ice-border there turned its currents much to the west from their former course. Proi!A1',i.e Origin of these Eskers. Although these two esker series, lying only a few miles apart, differ about 90^ in their trends, they were p'-obably formed at the same time or one very soon after the other, a: > "ght happen by diver- ij, Pkuc. Roch. Acad, ok Sc, Vol.. j, April, 1893. 194 ROCHESTER ACADEMY OK SCIENCE. [Jan. 9, sion of a glacial river from one avenue into another near its point of discharge from the ice-sheet. Each series seems to be attributable to deposition in the ice-walled channel of a stream of water flowing down from the surface of the melting ice-sheet, where the gravel and sand had been gathered from the previously er.glacial drift that had been exposed by ablation as a superglacial stratum. Near their mouths, or places of discharge to the land surface, these rivers appear to have flowed in valleys or gorges inclosed by unmelted plateaus of the ice-margin, upon which much drift rested. In some sections of our drift formations, as of Third and Fourth Cliffs in Scituate, Mass., which are partially eroded drumlins on the shore of the ocean, thick beds of stratified gravel and sand are found which were undoubtedly laid down by subglacial streams ('). But such beds formed under the ice-sheet are rare in most parts of the country, and the eskers here described and all others which have come under my examination of extensive areas in New England, and in Minnesota, northern Iowa, the Dakotas, and Manitoba, I believe to have been deposited in ice- walled channels open above to the sky. Before proceeding to consider more in detail the structure and materials of these eskers in their bearing on this view of their mode of accumulation, it will be desirable to notice former expressions of opinion as tc the origin of the Pinnacle hills. The earliest reference to this esker is by James Hall, in his report on the Fourth Geological Dis- trict of New York, published in i\. II, pp. 25S-265 ; \ ol. Ill, pp. 4^4-4^7- '■^93. 1 UPHAM— K.SKERn NKAK ROCHESTER, N. V. 199 beneath them. In like manner I have shown that certain eskers in New Hampshire and Manitoba were underlain by ice at the time of their accumulation and by its meltinj; away were afterward allowed t<, hink to the land. (') .ViM'Mc A riiiN ()!• riii> K.Mi.AN A Hon lo Eskers elsewhere. If eskers were subglacial deposits, we should e.xpect them to be often covered wholly or partly with the enyiacial drift, as bcuUders and loose deposits of till, which would be permitted to fall upon them when the ice-roof was melted away. Such a roof would be iiKjre or less overspread with the drift that had been c(jntained in the higher portions of the icesheet and was exposed on its surface by ablation. Sections indeed are occasionally found, where subylacial beds of modified drift have become covered by sub,t,^lacial and euglacinl till ; (') but these usually differ widely in their character from the torrential esker and kame deposits, which very rarely contain or bear upon their surface any considerable abundance of boulders or other drift mate- rials that have not evidently been transported, worn, and assorted by water. In nearly all the localities where I have observed boulders or masses of till imbedded within eskers or lying on their surface, the most probable explanation of their derivation has been by falling Irom the enclosing ice- walls of channels ojjen U> the sky, or by being brought while f"ozen in ice-lloes. ('') At only one place, in Dover, N. H., 1 have found a portion of an esker covered with a deposit of boulders and till which may have fallen from a melting ice roof, th(jugh another interpretation seems to me preferable. (*) A different view is taken by Professor W. M. Davis, who regards certain eskers in the vicinity of Auburndale, Mass., which 1 have repeatedly examined with him and other glacialists, as probably of sub- glacial origin. (') These eskers I think to have been formed in ice- walled channels, (jpen above and underlain by a slight depth of ice Extending southward from them are associated sand plains or plateaus, deposited just outside the ice front by the streams which produced the esker ridges. Professor Davis describes a backwardly dipping strati- II.) (iculciKV I't Nl'W lhiin|)shiie. Vul. Ill, 10713,141. 1.7,11''. (ie.jl. and N.it. lli-.l. Survey of C.uiaila, Annual Riiiort, iua -.crios, Veil. IV, for iSSKS'i, pp. .ij-^i E. i_-.i (;eolni;yot N. H., VmI. III. pp. i..S, 1 ii 1 -,7, -s,, 2..,i. OtoLiintl Nat. Mini. Survey ot Minne- sota, kiululi Animal Krp..rt, for 17,. pp. 11 ,, 114 ; Ein.il Rep^rl, \'ols. I and II. I'roceedingb of the Moston Soi.-jety of Natur.il History, \'ol. XXlV, i.i.-f), pp, -ni-s, 21.7-'). t i.l (ieoloyy of N. H,, Vol. Ill, pp. 4;, 4'% hs, if, ,,1, uJ, i-'7. Mi, i4«, liS. ■'«, ■''-■• CJeolo^y of Minn.', iMnal Report, Vol. II, p. 550. Geol. and Nal. Hist. Survey of Canada, Annual Report, Vol. IV, lip. 4'. 4J K. ,.;.i Geolouy of X. H., Vol. Ill, p. i,,. I ;i. liulletin, <;. S. A., Vol. I, pp. !.,,5 -sj:;, with -.ection-,. 1'roi.eedinK^ of tlie lioston Society of N'.itaral H\ ■■ iry, vol. XXV, i^jj, pp. 477-4JJ. 200 OCHKSIKR ACADIMV uK SCII' NCK. IJ m. 9. f the beds forming the edReof the plains where theyadjoinec the ice.sheet. and attribmen it t., the v.ptlow of siil);;lacial waters bringing with them the sediments whie.ii make the pla>n and reach to a considerable distance, having in their lower portion, on the greater part of their area, the forwardly dipping stratif.cation that is characteristic of deltas or of deposits swept by torrential currents into the slowly flowing broad expanse of lloo.led rivers. It seems to me. however more probable that the back-set beds were formed by the downward and backward transfer of sand from the surface of the plain, to till in succession the small spaces from which the ice-sheet was gradually withdrawn. P.ecause the summer melting of the North American loe-sheet m the Champlain epoch, or closing stage of the Ciacial period, was far more rapid than that of the Alaskan glaciers at the present day. the previously existing small subglacial stream-courses were inadeciuate for the transportation of the large supplies of englacial drift then set free by which, indeed, the" subglacial tunnels appear to have been mos'tlv obstructed and closed. The waters of the glacial melting and of accompanying rains therefore Howed. as I believe, in channels on the ice surface, often near their mouths more like canons than like ordinary land valleys, there depositing the eskers and kames. My studies of the Pinnacle hills and I'ittsford esker series, of the very massive kame deposits forming the greater part of the outermost terminal moraine on Long Island eastward from Roslyn ().."f J^l^^ large kame called the Devil's Heart, rising in a somewhat conical hill ,,. feet above the adj<.ining country south of Devil's lake in North Dakota and of the esker named liird's hill, seven miles northeast of Winnipeg C), seem to me to demonstrate, beyond all doubt, that their material, and probably likewise that of eskers and kames gener- ally was supplied by superglacial streams from the plentiful englac.al driVt, and could not have been brr.ught from drift beneath the ice by subglacial drainage. (11. (-'I. a;;;;,";:;:] n:^. \\i:'^;^:^^!r^^n:^^\^^^ ^^i:-. new senes, v,,,. ,v, .. ..ss. 8i), Pp! .!S-4.^ K. witli -.cctiun. I o in le te et ill ul