DISLOCATIONS OF THE COASTAL PLAIN STRATA. 5 



Passing several papers whose authors were absent, the next paper pre- 

 sented was — 



DISLOCATIOyS IX CERTAIN PORTIOXS OF THE ATLANTIC COASTAL PLAIN 

 STRATA AND THEIR PROBABLE CAUSES* 



BY AllTlIUIt IIOLLICK 



[AbsfracC] 



Kxtendinii: from Nantucket, ^hirtluis Vinovanl, tlirouLih lUock island, Gardiners 

 ishuKl, Long island, Staten island and northern New Jersey, there is a clearly 

 marked line or area of disturbance which presents many features entirely different 

 from those with whit-h we are familiar elsewhere. A portion has been considered 

 by Professor X. S. Shaler to represent mountain-making effects, while the writer 

 is satisfied that ice action has produced similar phenomena. 



From a careful study of the region as a whole, we are now in a position to state, 

 as beyond question, that this line of disturbance is coincident with the line of the 

 terminal moraine from Nantucket to northern New Jersey ; that the phenomena of 

 folding and crumi)ling in the Cretaceous and post-Cretaceous strata are only to be 

 found where the moraine has advanced over some portion of the former coastal 

 l)lain, and that these phenomena cease abruptly where the moraine bends away 

 from or finally leaves the plain. 



The wi'iter is of the opinion that one series of cause of effect has been instru- 

 mental throughout, and the question at issue seems to be which of the two theories 

 just referred to is supported by the greater weight of evidence. 



Beginning with ]Marthas Vineyard, we may consider the general structure there 

 as typical of the region elsewhere. The island consists essentially of a series of 

 hills in the north, composed of a core of Cretaceous and post-Cretaceous strata, 

 tilted and folded, flanked on the north and cai)i)ed on the to^) by bowlder till which 

 gradually merges into water-assorted material on the southern flanks and extends 

 over the plains beyond. The Gay Head escarpment is the most extensive section 

 across the line of disturbance which is anywhere exposed to view. 



Proceeding westward, we find a similar structure to exist on Long island, 

 although the exi)OSures are far more limited, but it is only necessary to imagine 

 Long island separated into parts by convenient north and south erosion channel, 

 in order to reproduce Gay Head indefinitely. 



On Staten island the facts are even of greater significance and interest. The 

 moraine crosses a portion of the coastal i)lain near the Nai'rows, thence bends 

 northward, rests on the Archean axis, and again enters ui)on the i)]ain a few 

 nnles finther wc-t. Throughout both portions of the moraine; where it rests on 

 the coastal plain evidences of dislocation and distortion are to be seen. J>etween 

 these i)orti«jns there is not the slightest indication of any disturbance and the 

 topograi)hy of the plain is level and uniform. This little area seems to have been 

 specially preserved as an ol^ject-lesson in this connection. 



In northern New Jersey the evidences of disturbance are not so manifest, which 

 may i)erhaps be accounted for on the sujjposition that the ice, having advanced 

 over this portion of the plain from a comparatively level area, did not i>low down 



♦The |).i|)er wiis illiistraU'd l>y cliarts and maps of the rogion under discus.sion and by sketches 

 of many of the localilk-s luiuitioned. 



