loO N. S. SHALER — DEPOSITS OF EASTERN MASSACHUSETTS. 



during the lasl ice epoch. It therefore does not seem tome possible that 

 the pebble could have been driven down iuto the superficial portion of the 

 old conglomerate by the recenl glacial action. It should furthermore be 

 noted that the ancienl conglomerate contains a great number of hypogene 

 bowlders which have the same general lithological character as those which 

 wen- transported to this region from the Narragansetl basin during the lasl 

 glacial period. On the supposition thai tins old conglomerate is of either 

 Mine. -in' or Pliocene age it thus becomes mure probable than before thai it 

 i- of glacial origin. The fragment in question is about * by 5 by 3 inches- 

 and weighs aboul ten pounds. 'Before attacked by decay it was evidently 

 of an angular form, such as usually characterizes the pebbles of this very 

 hard material even where they have been transported for the distance of 50 

 miles or more. It seems impossible thai it could have owed its carriage to 



water action, and it therefore affords importanl additional evidence to prove 

 the glacial origin of the deposil in which it occurs. 



Assuming that the bowlder beds containing the erratics from the Narra- 

 gansett basin arc of glacial origin, the question manifestly arises whether 

 this deposit can be regarded as equivalent in age to the deposits formed 

 during the firsl advance of the ice over the central portion of the continent. 

 bul which have hitherto not been clearly observed in New England. It is 

 .-till too soon to decide this question. It may he noted, however, that it' 

 we regard the above named deposit- at Gay Head a- belonging to the lasl 

 glacial period, we are called on to assume the occurrence of a very great 



interval between the first and se< 1 advances of the ice. tor the extensive 



subaerial topography of Martha's Vineyard was evidently developed after 

 these lied- had been deposited and uplifted into their present attitudes. 



I >i i wi.kd Description of 8e< tions. 



The accompanying illustration ( plat.- '.» i contains three sections: the upper 

 fig. 1 a diagrammatic and partly ideal section from Vineyard sound south- 

 eastward to the valley ..f Ti-burv river neai- the point known a- the upper 

 I ' idier pond : the middle (fig. 2), divided into three parts, shows the section 

 of the beds in the Gay Head escarpment so far as they have been interpreted ; 

 while the small diagram at the bottom of the plate (fig. 3) affords a theo- 

 retical interpretation of a certain puzzling section of the escarpment. 



The first section I fig. 1 ) is intended to indicate tin- evidence which 3erV6fl 



to -how that the drainage of tM- country had been completely developed 

 before the advance of tin- lasl glacial sheet. It will be observed that the 

 glacial detritus forms hut a thin coating "ii the lower ridges, and ha- .i 

 thickness of only about 20 feet on the higher. At the point selected the 

 glacial waste forms a much thinner -he. t than i- usual in this part of the 



