1022 



HISTORICAL GEOLOGY. 



overlj'ing beds, which shoved aside and forced out the wet and mobile clay. At many 

 places along the coast the clay has been forced out in this w^ay and now covers more or 

 less of the slope below ; and in the clay -pits, sinking and exclusions are not uncommon. 

 At the Holmes clay-pit on Eresh Pond, near North^jort, there were cracks in 1875 at the 

 top of the bluff where the suiking was in progress, aud where, as the proprietor stated, 

 it had amounted to 16 inches in 20 months, and the movement, he added, was all the time 

 going on. A clay -bed is made to vary greatly in thickness in the face of a bluff because 

 locally squeezed out. 



1572 



1572-1575. 



1573 



1574 





1575 





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Sections of the Cretaceous and overlying beds on the north side of Long- Island. Figs. 1572, 1578, Sections near 

 Brown's Point, Petty's Bight; 1574, Section Similes south of Oyster Point; 1575, Section exposed by a storm 

 200 yards south of Brown's Point. W. W. Mather. 



In the case represented by Fig. 1575, the position of the beds plainly proves, as Mather 

 states (page 249), that an upturning and a subsequent denudation had taken place after 

 the lower beds of alternating clay and sand had been formed, and before the deposition 

 of the overlying clay-bed and the higher deposit of "coarse materials and bowlders" or 

 drift. The tilting in Figs. 1572-1574 probably had the same origin. The age of the clay- 

 bed C. I. in Fig. 1575 is left uncertain ; but the upturned beds are Cretaceous. Mather 

 states that in all sections the overlying drift deposits have the same horizontal position, 

 and that some of the bowlders contained in them have great size. "Blocks of 50 to 500 

 tons are not uncommon on the island" (page 174); and he reports one having an esti- 

 mated weight of 2000 tons. 



The upturned beds in Desor's Nantucket section, referred to on page 983, are covered 

 by others in horizontal position, and are probably of the same age and origin with those 

 of Long Island. 



On Martha's Vineyard, according to Shaler, the upturned beds, which include the 

 Cretaceous and Tertiary, bear evidence in their erosion that the chief upturning preceded 

 the Later Glacial epoch, if not partly at least the earlier. Lyell, in his Travels in North 

 America (1845), describes the sections at Gay Head and Chilmark, figures the former 

 (i, 204), and states that the upturning occurred between the Miocene Tertiary and the 

 "Boulder " or Drift period. 



There is grandeur in the simplicity as well as vastness of the movements 

 by which the earth was made ready for its latest stage. Equally simple and 



