Ground Water in the Norwalk, Suffield, and Glastonbury Areas, Connecticut

Some of the till, particularly that part below the weathered zone, is very tough, as is indicated by the popular term "hardpan" often applied to it. The toughness is in part due to its having been thor- oughly compacted by the great weight of the ice sheets, and in part to the interlocking of the sharp and angular grains. It seems prob- able that the more soluble constituents of the matrix have to some extent been dissolved by the ground water and have been redeposited in such a way as to cement the particles together. The relative amounts of the different sizes of material are shown in the following table.^ The material treated by mechanical analysis » Dorsey, C. W., ^nd Bonsteel, J. A., Soil survey in the Connecticut Valley : U. S. Dep-t. Agr. Div. Soils Field Operations for 1899, p. 131, 1900. \VATi;i;-Bi:Aii i -n >. ; J( )H.mations. 21 is the fine earth that roniained after the coarse gravel and bouUlers luul hoon reniu\ed. The lirst three analyses n'i)re^ent till derived in large part from Triassic sandstone and shales; the fourth a till derived from crystalline rocks. The boulders and pebbles mixed with the fine eartli (tlic matrix) constitute from 5 to 50 per cent or ('\ en more of the total vohimc. Mahuniial <tu<ilijxi s of t<tij>iy loams (tiU .so/7.s). milliineters. »ira\('] C;iarse sand . . . Medium sand.. Fine mmi VtTV fine sand. 8il*: Fine silt Clay Iy()ss by drying at. UoT. Loss on ignition 2-1 1-0. .5 0. .5-0. 2 0. 25-0. 1.5 0. 1-0. 0.5 0. a5-0. 01 0. 01-0. Oft5 0. 00.5-0. 0001 1 2 3 2 12.4.5 5.26 3.3.5 11.86 8.66 S.60 13. 98 18. 83 31.2.5 14. 7.S 21.00 34.22 17. .51 IS. 83 4.3-5 S.20 8.70 6.20 8.67 .5.30 (i. .57 10.23 10. 87 1.36 1.04 1.01 2.03 l.(J9 1.77 3. o."; 3.8.5 8.22 11.. 53 29.82 21.26 6.45 12.20 1.54 2.35 1. Stony loam fixini Triassic rocks half a milo south ol Bloomlielil, Conn. 2. Stony loam from 'Trias.sic rock-:, Enfuld, Conn. 3. Stony loam from Trins.sic rocks 13 miks south of Hazard villo. Conn. 4. Stony loam from cr\stalline rocks 2 miles south of Ash]cy^"ille, Mass. The water-bearing capacity of tlie till is difficult to estimate for any large area because of its extreme variability. A small sample may be tested by drying it well, then soaking it in water until it is saturated, and finall}^ allowing the excess to drain away. A com- ]>arison of the weight after drying with the final weight will show how much water has been absorbed. Gregory ^ made such an experi- ment on a typical mass of till collected near New Haven, Conn., and determined that 1 cubic foot could absorb about 3.45 quarts of water. In other words, the till is able to absorb water to the extent of 11.55 per cent of its total volume. Other samples would undoubtedly show higher and lower results, but this is prol»ably not far from the average. The pores of the till are relatively small, so that water does not soak into it very rapidly. On the other hand, the pores are very numerous and are able in the aggregate to hold a good deal of water, as shown above. The fineness of the pores is a disadvantage in that it makes absorption slow\ but it is at the same time an advantage in that it retards the loss of water by seepage. The till of Con- necticut is more pervious than that of many other glaciated regions, because the hard, resistant rocks from which it w^as largely derived yielded grains of quartz and other siliceous minerals rather than fine rock flour. ' Gregory, II. E., and Ellis. E. E., Undorirrounrl-water sources of Connecticut ; U. S. Geol. Survey Watei-Supply Paper 232, p. 139, 1900. 22 GROUiNl) WATER IX aSTOEWALK , AI\D OTHER AREAS, COjSriT. At many places there are lenses or irregular masses of water- washed and stratified material within the unsorted and iinstratified till. These were presumably deposited by subgiacial streams that existed but a short time before they were diverted or cut off by the forward movement of the ice sheet. The lenses are of considerable value where they happen to be cut by a well, as they in effect increase the area of till tributary to the well and so a,ugment its supply. Well diggers often report that at a certain depth they " struck a spring." Such reports probably refer to cutting into lenses of this type. The till has no striking topographic expression. The plastering action of the ice sheet by which it was deposited tended to give it a generally smooth, surface. In a very few places there are ridges or terrace-shaped masses of till built as lateral moraines along the flanks of tongues of ice that protruded beyond the front of the main ice sheet. In many places the till was heaped up beneath the ice sheet to form drumlins^^ much as sand bars are built in river chan- nels. The drurnlins are gently rounded hills and may or may not have cores of solid rock. STRATIFIED DRIFT. In contrast with the till, which was formed by direct ice action, is the stratified drift, a water-laid deposit. Stratified drift may have originated either v/ithin, on, under, or in front of the ice sheet. In Connecticut only subgiacial and extragiacial stratified drift are found, and except for their topographic expression these two types are very similar. Stratified drift is composed of the washed and well-sorted, re- worked constituents of the till together with some debris made hj the weathering and erosion of bedrock. The water that did the work was for the most part the melted ice from the glacier. Since glacial time the streams have in places added to the deposits of stratified drift, but elsewhere and probably to a greater extent they have eroded and removed parts of those deposits. The distinction between the glacial stratified drift and the more recent stream allu- vium is hard to draw, and although the latter is a little less clean and yields a little less water, the distinction need not be drawn for a ground-water study. The mapping and separation of mappable units within the glacial drift in this report is based in large part on the capacity of the material for carrying' water. A different basis of mapping might be used in a report made for some other purpose, Near the end of the glacial epoch the climate became mild and vast amounts of ice were melted. The relativelv soft till was WATi:U-r.i:AUlX(i FOKIMiVTIONS. 23 easily eroded and supplied a tiivaL abiaulaiice of debris. Some of the .streams flowed in sinuous subglacial channels, in wliich they made deposits that have now become the long, winding ridges called cskors. The water in some of the channels beneath the ice was uiuler hydraulic liead, as is shown by the fact that some eskers cross ridges and gidlies regardless of the grades. Where the debris-laden waters came to the edge of the ice sheet kames were made. Some of the material was carried beyond the front of the ice sheet and was laid down as an alluvial deposit in the \alleys. Xot all the materials composing the wide outwash plains have been deposited by running water. There are also beds of finer material — clay and silt rather than sand — that were laid dovv-n in lakes and ponds which stood in shallov/ depressions in front of the ice. The stratified drift consists of lenses and beds laid one against another in a very intricate and irregular way. Some of the lenses consist of fine sand, others of coarse sand, others of gravel, and still others of cobbles, but the sands are the most abundant. The material of each lens is rather uniform in size, but there may be a gi'eat difference between adjacent lenses. In general the finer materials form more extensive beds than the coarser. Some of the beds of clay and fine silt, though only an inch or two thick, have a hori- zontal extent of hundreds of feet. Lenses of gravel may be 2 or 3 feet thick and not extend over 10 feet horizontally. The sand lenses are composed almost entirely of quartz grains. In the gravel lenses are pebbles of many kinds of rocks. The clay beds consist of trvie clay, thin flakes of mica, and minute pirticles of quartz and feld.spar. All the deposits contain iron, which gives them brown colors. The following analyses^ show the character of the stratified drift : Meelianlcrtl anah/scs of yfratipeel (irift. Diameter in millimeters. 1 2 3 4 5 Gravel 2-1 1-0.5 0. .5-0. 25 0. 25-0. 1 0.1-0.05 0. 05-0. 01 0. 01-0. 005 0.005-0.0001 4.98 11.31 33. 41 33.75 10.82 2.09 1.03 1.65 .50 .80 2.20 7.51 3:3.50 ^ •i2.05 13. 50 4.47 1.75 2.7S .80 1.30 0.50 1.51 7.96 23.27 41.82 9.15 6.32 4.40 1.92 3. 68 0.00 Trace. .21 1.50 19.55 33.67 28.54 9.50 2.60 4.75 0.00 .29 .40 .73 Silt 32. 57 Fine silt 29.10 Clav 25. 65 Loss on drying at 100° C 2.17 3.53 1. Coarse, shnrp sand 2 milos souih of Bloomfield. 2. Sandy loam soutiiwest of Windsor. 3. Fine sandy loam half a mile nortiieast of South Windsor. 4. Recent flood-plain deposits three-fourths of a mile southeast of Ilartrord. 5. Briekclay from glacial lake Lcds. hHifReld. Dor: cy, C. W., and Bonstoel, J. A., op. cit. 24 GROUND WATER IN NORWAI.K AND OTHER AREAS, CONN. The most striking difference shown by a comparison of this table with the table of mechanical analyses of till samples (p. 21) is that in each sample of stratified drift almost all the material is included within two or three sizes, whereas in the till there is a wider diversity of sizes, even exclusive of the boulders, which were taken out before analysis. The topographic form assumed by most of the stratified drift is that of a sand plain, which may be modified by terraces, by valleys cut below it, or by kettle holes. In the highlands small bodies of stratified drift form eskers — long, winding ridges, 10 to 40 feet high, in some places with narrow crests and in others with flat tops, and generally with steep flanks. In the lowlands there are kame areas, which consist of hummocky hillocks and short ridges of stratified drift irregularly scattered. CRITERIA rOR DIFFERENTIATION OF TILL AND STRATIFIED DRIFT.