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SURFICIAL GEOLOGIC MAP of the ASHLEY FALLS QUADRANGLE, MASSACHUSETTS-CONNECTICUT by G

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SURFICIAL GEOLOGIC MAP of the ASHLEY FALLS QUADRANGLE, MASSACHUSETTS-CONNECTICUT by G jivuubiTY LIBRARIES POCKEi DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY PREPARED IN COOPERATION WITH THE COMMONWEALTH OF MASSACHUSETTS DEPARTMENT OF PUBLIC WORKS AND THE STATE OF CONNECTICUT GEOLOGICAL AND NATURAL HISTORY SURVEY ft il \\d I:.vy let ft GEOLOGIC •ft ;-'^--^: - QUADRANGLE MAPS OF THE ft 1 C ft ft . S ft UNITED STATES til ft ft 2 m ft SURFICIAL GEOLOGIC MAP ft ft OF THE ft ASHLEY FALLS QUADRANGLE > ft ft CO MASSACHUSETTS-CONNECTICUT ft I By ft G. William Holmes and Walter S. Newman ft ft . > CO CO O zo r o > O r 2 O o a o o jQUADRANGLE LOCATION o oQ MINERAt. GEOLOGIC QUADRANGLE PREPARED IN COOPERATION WITH SURFFC1AL GEOLOGY THE COMMONWEALT HOF MASSACHUSETTS DEPARTMENT OF PUBLIC WORKS AND ASHLEY FALLS QUADRANGLE, MASS.-CONN. DEPARTMENT OF THE INTERIOR GQ-936 UNITED STATES GEOLOGICAL SURVEY THE STAT EOF CONNECTICUT GEOLOGICAL AND NATURAL HISTORY SURVEY OJGfl III 73° 15' (GREAT BARRINGTON) 5 42 'O~'3O'' INTRODUCTION The next recorded ice-front position is in the Konkapot Val- EXPLANATION The main topographic elements of the Ashley Falls quad- ley about 2 miles north of the Massachusetts border and just rangle include parts of the Berkshire Hills on the east and the south of Konkapot crossroads. Here a small ice block lay at A layer of windblown sitt and sand, locally mixed with frost-disturbed Ilousatonic Valley and the Taconic Mountains on the wyst. the head of a kame terrace, kame (Qcd3), outwash (Qo), and rock fragments, covers part of the surficial deposits but is not shown Many of the valleys and ridges appear to be controlled by the stream-terrace (Qsta) sequence which extends uninterruptedly structure and lithology of the bedrock, although glaciation has from an elevation of about 700 feet above sea level in a broad modified the landscape. Features associated with giaciatiun in- arc to the Housatonic Valley. Textures of this sequence of de­ Qal clude drumlinoid hills, a large delta, kames and kame terraces, posits decrease in size down valley from coarse gravel to sand, and lake-floor deposits. There is no evidence in this quadran- and collapsed and uneven bedding gives way to uncoilapsed Alluvium gle for more than one glaciation; this glaciation, on the basis of and even budding. The downstream edge grades to a sandy, Yellowish-brown, ycllutvish-Tcd. dark'brown, and dark-gray-brmtm gravel, regional evidence, is probably late Wisconsinan in age. Dur- silty composite stream terrace in the Housatonic Valley, which «64 sand, »»//, ami cltty-irizc material. Moderately to well sorted. Moder­ ing deglaciation, wastage of stagnant ice proceeded generally in turn is graded to the Great Falls bedrock threshold near ately to well Klrati/icd. Occurs in siualca awl in flood plains and low terrace* which arc imtndnted every few decades. Typically 10-12 ft from south to north, and glacial melt water was temporarily Falls Village, Conn. This relationship implies that during or above stream level in the Hmtsatovic Valley. Thiclmess typically 75 ft. impounded in the Blackberry and Housatonic River valleys. before the deposition of this sequence, the main Housatonic Generally derived from strcam-tcrracv deposits, lacustrine deposits, and Features that formed in late glacial and (or) Holoccne time Valley was drained of lake water, and stream-terrace deposits till. Scored by meander scars and swales, and locally mantled 6?y or­ include stream-terrace deposits, alluvial-fan deposits, land- formed more or less concomitantly with the outwash deposits 4100C0 F-TET ganic deposits. Underlain by Pleistocene lacustrine deposits in the (MAS5.J Hoitsaiovic Valley n-nd locally in the Konkapol Valley. Soil develop­ slide debris, and talus. of the sequence. ment is minor QUATERNARY HISTORY As stated above, stream-terrace deposits were laid down in the Housatonic Valley while stagnant ice features formed in During at least the final episode of ice movement, glacial ice the tributary valleys. Some of these Housatonic deposits are Of crossed the ridges and valleys in a southeasterly direction, as complex. Their lower sections locally are lacustrine in origin, shown by striae and grooves whose orientations range from and the surface material, mostly sand, is derived from glacio- S.25"E. to S.til°E. This southeasterly direction of ice move­ Alluvial-fan deposits Swamp deposits fluvial material of various ages from the tributary valleys and Gray to gray-brown, snbronndcd to angular, sttnd, Black and brown-hlack silt, clay-size material, and ment is also indicated by the orientation of a few drumlinoid from the upper Housatonic Valley in the Great Barrington and gravel, and boulders, poorly stratified and poorly pent, moderately well sorted avd well to poorly strat­ hills and the distribution of erratics from unique bedrock Stockbridge areas. Subsequently, theso deposits were trenched sorted, in gently sloping fans graded to strea:-.-ter- ified. Occui's on alluviu?n, stream-terrace deposits, sources within or immediately north of the quadrangle. One about 20 feet. Stream-terrace deposits on minor streams are race deposits and alluvium. Occurs as mttck as 20 water-laid iee-co7ttucl deposits, till, and lacustrine source of erratics is June Mountain where the garnet schist ft above stream level. Materials derived frcm till deposits. Thickness from less than lflto more than composed of gravel and, locally, boulder gravel and have been and local bedrock (schist, gneiss, and quartzite) 4fl; measured thickness averages slightly marc than fades of the Walloomsac Formation of Ordovician age crops incised 10 to 20 feet. aft. Locally contains small pcbblvs out northeast of Sheffield Center in the Ashley Falls and Great Barrington qimdranglos. Large crraLics of Ihu June Mountain Modern flood-plain alluvium (Qal), mostly silt and fine sand, facics tie in a crude fan-shaped area southeast of their source was deposited in the Housatonic Valley after trenching of the Qst. outcrops. East of Smith Hollow, blocks lie on both sides of the stream-terrace deposits. Alluviation is a continuing process, road in a well-defined train. Blue-quartz gneiss, another lo- as major floods every few decades inundate the flood-plain alluvium, reaching or barely exceeding the level of the stream­ cally unique erratic source, occurs on Brush Hill. Southeast Qst of this outcrop area are scattered boulders of gneiss which terrace deposits. As suggested by profile A-A\ net accumula­ 3 have been traced across the Konkapot .River south of Mill Riv- tion is minor, and downcutting is limited by the bedrock thresh- er IN. M. Ratcliffe, written commun., IMS). old at Falls Village, Conn. Along smaller streams, recent al­ Outwash deposits luviation is minimal and is mostly confined to reworking of the Qst* Ught-yclloivish-brown gravel, pebble Till-fabric determinations support in part these data on ice stream-terrace deposits during major floods. sand, and sand, moderately well movement. Two till-fabric determinations, at points Cand D sorted and stratified, generally not on the map, suggest ice movement from the north-northwest Organic deposits have developed in postglacial time in poorly showing channel fillings or collapse drained areas, resulting in widespread but thin deposits of peat structures. Clasts subrowuled to and from the west-northwest, respectively. At two other Qst, rounded. Occur as broad terrace points, A and B, till fabrics are oriented generally north and mixed with silt and clay-size material. Postglacial solution in which viergcs upstream with ice­ carbonate rocks, such as on the west slope of Benton Hill, has ; east-northeast, respectively. The latter two apparently anom­ • :Qed;1 J Stream-terrace deposits contact deposits (Qcd -,} in the Kon­ formed sinks and solution-enlarged joints. Solution has also Lighl-gra-y-brown, dark-yeiloioish­ kapot area, and which merges alous orientations may have been the result of mass move- downstream with stream-terrace produced sinks and disappearing and reappearing streams in brojtm, reddish-brown, liaht-aray, Delta deposits Lake-floor deposits ment on the till slopes. Thus, it appears that ice flow, at least Water-laid ice-contact deposits or ^olive-gray sand and silt, in deposits (Qst3). Typically 20-30 the area north of Brewer Branch Road. and ice-channel deposits Yellowish-brown pebble sand, sand, ft thick and 20-30 ft above present Gray to gray-brown clay, silt, and during the last phase of active movement, was in a general ;ilaces containing pebbles, gravel, sand, moderately xoell sorted, southeasterly direction, which agrees with indications of ice Mass movement formed talus sheets on Toms Hill, small Light-ycUoidsh-brown or yelluvntsh- mill boulders. Moderately well (f nd gravel of mixed sizes. Topset streams beds mostly gravel, moderately well poorly to well stratified, occurring movement throughout the Berkshire Hills and Taconic Moun­ landslides on Rattlesnake Hill, and scattered talus blocks (un­ brown cobble gravel, pebble gravel, sorted and well to nonslratified. in very small outcrops in stream, mapped) on the slopes of Canaan Mountain. Most of this ma­ and pebble sand, viodcratcty to Oer-H-rs tw varrow to nridc.flal to to poorly sorted, and not well strat­ tains of Massachusetts. ified. Foreset beds mostly sand, banks or south of the East Canaan terial appears to be stabilized, and hence it probably was de- poorly sorted and stratified; eon- gnitly sloping and, in part, gently delta at the surface; extensive be­ Evidence of glacial scour and erosion is minimal on the pres- tains collapse stntctures, r.hnmwl rolling terraces. Typically 20-25 •moderately well sorted and strat­ posited during the waning phases of glaciation. fillings, kettles, depressions, and ified, with channel fillings. Fore­ low flood-plain deposits and sent topographic surface, However, the valley fill in the Hou­ fl above present streams and as stream-terrace deposits (noit shown satonic Valley includes glacial-lake deposits to depths of 242 ECONOMIC GEOLOGY bodies of flow till, ntirf, rarely, much as 60 ft thick.
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