OLD TILLS 



515 



The bed-rock at this place is a nietamorphic schist, on which rests 4 to 

 12 feet of a hard, much oxidized, bright 3'ellow till, made ixp large!}' 

 of the underlying schist, but containing some foreign pebbles. Overlying 

 it are 1 to 5 feet of a somewhat oxidized till containing numerous foreign 

 pebbles. Above these tills is a stratum of 2 to 5 feet of fine white sand 

 which has been considerably contorted, evidently by the weight of over- 

 lying ice, which deposited 1 to 6 feet of clayey and bouldery till which 

 forms the surface. The surface deposit is oxidized for about 2 feet at 

 the top. 



The lowermost drift deposit in this section has the appearance of a 

 very old till, its difference in character, its high degree of oxidation, and 

 its position indicating that it was not deposited by any slight oscillation 

 of the Wisconsin ice frgnt. The same beds were seen in a cellar excava- 

 tion near by. 



Figure 2. — Section in Railroad Cut at South Lawrence, Massachusetts. 



Showing deposits of old till. A, bed-rock ; B, hard, much oxidized till, made up 

 largely of underlying schist ; C, somewhaj; oxidized till containing many foreign pebbles ; 

 D, fine white sand, with contorted stratification ; E, clayey, bouldery till, oxidized about 

 two feet at the top. 



Exposures at Portland, Maine. — In a sand pit one-fourth of a mile 

 north of Union station, Portland, there are extensive exposures of sand 

 and gravel overlain by clay. At one point here a peculiar feature was 

 exposed in June, 1906. This is illustrated in figure 3. The hard, com- 

 pact, light gray to dark brown, blocky clay rested on an unconformity, 

 below which was 3 feet or more of a horizontally stratified glacial sand- 

 stone containing a few boulders, mostly of similar material, up to 2 feet 

 in diameter. The sandstone was very solid and resistant, cemented by 

 iron oxide. Below this occurred 2 feet of stratified sand and fine gravel, 

 oxidized very yellow and resembling certain yellow sands seen in connec- 

 tion with pre-Montauk drift underneath drumlins at Scituate and Ply- 

 mouth, Massachusetts. The pebbles in this bed were much decomposed 

 by weathering, only those composed of quartzite remaining solid. The 

 only granite pebble that could be found was 2 inches in diameter and was 

 stained to the center. The weathering and erosion of the sands before 

 the deposition of the clay indicate an intervening elevation of some dura- 

 tion. A thorough search was made for another and better exposure of 

 the deposit, but none could be found. 



