PLEISTOCENE FORMATIONS OF SANKATY HEAD 733 



This theory, then, in its entirety, cannot be reconciled to the facts, 

 and must be modified in some particulars. 



The following hypothesis is presented as being in accord with 

 all the phenomena observed, and probably coming nearest to the 

 truth in an exposition of the history of these deposits: 



At the beginning of this deposition, a precipitous shore probably 

 stood to the north of the lagoon, or the lagoon itself may have been 

 in the nature of a basin-shaped inlet, open to the south, and sur- 

 rounded by steep shores of which the deeply dipping lower clay 

 formed the portion below sea-level. A variety of material derived 

 from this old shore by the encroaching sea before the outer bar was 

 formed, was spread over the bottom of the basin, assuming nearly 

 the dip of the surface upon which it was deposited, the dip becoming 

 less and less as the basin became filled. This agrees with the coarse 

 nature of the lower deposits, and the irregular bedding noticed. 

 One of the lower ferruginous gravels (No. 2) was found to increase 

 from 3 inches to 1 foot in thickness within a distance of 3 or 4 feet 

 to the south. The dip is in the nature of a false dip, the deposits 

 resembling very much in structure those fan-like non-marine accu- 

 mulations in which the dip decreases in passing upward through 

 the successive layers. We may consider then that the dip is an 

 initial one, and not caused by a subsequent folding of the strata. 



The lower white sands (No. 5) probably represent the washing 

 in of some seaward material, and giant ripple marks, such as would 

 be made by ocean waves, were found on the upper part. The lignite 

 found in this bed is no doubt derived from seaweed and driftwood. 



The lagoon or inlet now became well protected from the open sea 

 by the development of the outer bar or barrier beach, and the upper 

 clay of No. 6 became deposited from landward washings, on the 

 floor of the lagoon. This now became the home of shoal water 

 animals, as evidenced by the species which have already been enu- 

 merated. How long these conditions lasted it is of course impossible 

 to tell, but they were brought to an end before the deposition of the 

 upper beds. As these upper beds were formed, a subsidence of the 

 land in this region was taking place, and no doubt connected with 

 the advance of the huge mass of the Wisconsin ice-sheet. The water 

 became colder, the southern fauna was driven out, and deeper-water 

 northern, and even arctic species were present, and included in the 



