COARSE GRAVELS 527 



overlain imconformably by marine clay. The following is a sample sec- 

 tion exposed in the western part of Waterville, Maine : 



Section of Sands and Gravels at Waterville, Maine 



Material Feet 



5. Unstratified and seini-stratifled clayey gravel (Wisconsin till ?) 2 to 6 



4. Stratified clay 4 to 6 



3. Stratified sand 2 to 5 



(Unconformity.) 



2. Poorly stratified gravel 20 



1. Fine brown sand 5 + 



40 + 



The following section is exposed near the bank of Penobscot river, in 



Brewer, opposite Bangor : 



Section at Breiccr, Maine 



Material Feet 



2. Till, containing many boulders up to 2 feet in diameter 4 to 7 



1. Horizontally stratified sand and gravel 35 



Relations and correZa^ions.-^— The gravels are also well exposed at Port- 

 land and at Augusta, and probably at many places where they have 

 not been recognized. They have not been seen anywhere to rest on till, 

 but there is no reason for doubting that they are more recent than one 

 or more till deposits. They are commonly overlain l)y clay, as at Au- 

 gusta and Portland, and numerous borings and wells at Boston, Cam- 

 bridge, Lynn, and in the Merrimac valley obtain water in gravel after 

 penetrating clay. At Augusta and elsewhere the gravels can be seen to 

 be overlain by Wisconsin till. The gravels have been greatly contorted 

 in places, and the contortion can not be explained except by the theory of 

 an overriding ice-sheet (see page 528). In age these gravels are believed 

 to date from the beginning of the "Second Interglacial epoch" of Wood- 

 worth* in southern New England, and perhaps to correspond with the 

 retreatal deposits of the Illinoisan in the middle West. 



Distinction from Wisconsin gravels. — In most localities these gravels 

 can not be distinguished readily from Wisconsin. In some sections, 

 however, the evidence that they are of pre-Wisconsin age is very striking. 

 This evidence is of threefold nature, as follows : 



1. Probable erosion before deposition of overlying (pre-Wisconsin) 

 clay. 



2. Oecnrrence of till overlying the gravels. 



3. Erosion and folding of gravels by overriding ice. 



1. Erosion before deposition of overlying clay. — Evidence pointing to 



• Seventeenth Ann. Rept. U. S. Geological Survey, 189C, pp. 975-988. 



