730 J. HOWARD WILSON 



of which Sankaty Head is the eastern extension do not represent 

 the southern limit of the ice-sheet at this point. It was found that 

 the ice maintained a quite stationary front some three miles farther 

 to the south, forming the well-developed contact slope which runs 

 in a northwesterly direction from Tom Never's Head. 



The writer held the same opinion in regard to these Sankaty 

 Head deposits at the beginning of the work, the beds at that time 

 presenting a very confused appearance, which was found later to 

 be due to a superficial disturbance with a mingling of talus. When 

 the disturbed portion was finally removed, however, the beds were 

 found to present very characteristic and constant characters. That 

 these beds could not owe their origin to glacial action, but are normal 

 marine deposits, seems to be certain for the following reasons: 

 (i) Numerous delicate, perfect, and unworn shells occur. (2) 

 Numerous bivalves, already mentioned in the description of the 

 beds, were found in the natural position in which they lived, with 

 both valves together, and, in the case of Venus, with even the liga- 

 ment in place. (3) There is no mixture of faunas, as would be the 

 case in the redeposition of material from different beds. The three 

 lower beds contain fossils which have a distinctly southern range, 

 and are of a shallow water type; while the upper beds contain a 

 decidedly northern fauna, many species being characteristic of arctic 

 seas, and of considerably deeper water. Such conditions can hardly 

 be explained except by supposing these beds to be in their original 

 positions. 



In view of the phenomena observed, and the facts ascertained 

 in regard to these deposits, it would seem that an attempt might be 

 made toward an explanation of their history. The lower clay noticed 

 by early observers is probably identical with the yellowish-brown 

 clay found elsewhere on the island, generally more or less covered 

 by the glacial drift. This clay is apparently an old till of pre- 

 Wisconsin age, and which, modified by erosion, formed the land 

 surface of hills and valleys in this region before the advance of the 

 last- ice-sheet, which buried it under a heterogeneous mass of drift. 

 At this time shallow inlets probably occupied some of the low areas 

 between the higher land surfaces, or lagoon-like bays were to be 

 found at points along this old shore, protected from the open sea 

 by bars or low barrier beaches. 



