286 • G-LACIAL GRAVELS OF MAINE. 



Since 1861 Prof. C. H. Hitchcock has repeatedly expressed the belief 

 that two advances of the ice are proved b}' the relations of the iipper till 

 to the fossiliferous marine clays at Portland.^ The same opinion has been 

 expressed in the geological reports of New Hampshire. Professor Hitch- 

 cock's latest conclusions are contained in his report as a member of the 

 American Committee of the International Congress of Geologists:^ 



* * * Very clear evidence of the relations of the fossiliferous beds to both tills 

 is found at Portland, Maine. Here clays and sands rise about 100 feet above the sea 

 and hold 121 species of organisms, all of living forms. They rest upon typical lower 

 till, and are overlain by as much as 50 feet thickness of upper till. At the time the 

 reporter described these facts the jirevaleut doctrine of the trij^le nature of the glacial 

 period had not been established; but it seems clear that two seasons of ice iiresence 

 are indicated at this locality. * * * 



The meaning of the terms "interglacial," as well as "upper" and 

 "lower" till, imist be made definite when used in this connection. The use 

 of the term interglacial as of world-wide application can not be warranted 

 until the facts are all in; for the present it can only be admitted to express 

 the facts in particular regions explored, e. g., the Mississippi Valley, large 

 parts of Europe, etc. At the great terminal moraines there may have been 

 many advances and retreats of the ice, and one studying the till there 

 might come to the conclusion that there had been many glacial and inter- 

 glacial periods, and so there would have been at his place of study and 

 from his standpoint; yet all these advances of the ice might be comprised 

 within what another would consider as a single invasion of the ice, mere 

 minor accidents of a larger movement. So, too, the term "upper'' till may 

 mean englacial till, or, where there are tills deposited during two distinct 

 advances of the ice separated by a warmer climate, it may mean the later 

 of these tills. The use of the term b)^ Professor Hitchcock in connection 

 with the reference to the triple nature of the Glacial period seems to indi- 

 cate that he considers the two seasons of ice presence at Portland as the 

 correlative of the two glacial epochs of the interior. 



Let us review the points brought out by Professor Hitchcock: 

 1. The locality cited is situated at the western end of Portland, where 

 there have been extensive landslips, and it is difficult to determine what was 

 the original order of deposition. The proof of so important an event as an 



' Thus, in the Preliminary Report upon the Natural History and Geology of the State of Maine, 

 1861, p. 275: "We have recently noticed that iu Portland these clays underlie a coarse deposit, which 

 has always been referred to the unmodified drift," etc. 



-Am. Geol., vol. 2, p. 302. 



