TREND OP AXES OF DISTURBANCE. 449 



adverted to the fact that the dislocations at Gay Head have led to the de- 

 velopment of axes of elevation having at that pointa prevailing northwest and 

 southeast direction. It should be made clear that later studies on the island 

 have shown that this axial direction is not maintained throughout the area 

 of the island. The greater part of the beds in the towns of Chilmark and 

 Tisbury exhibit a northeast and southwest trend. It thus appears likely 

 that the dislocations of this time present a considerable variety in the axial 

 direction of the folds, a portion of them departing widely from the prevail- 

 ing strikes of the eastern portion of North America, while the larger part 

 conform to that general axis. 



Glacial Origin of Bowlder Beds Containing Fragments of the 



Osseous Conglomerate. 



Among the more important results obtained in the later studies on the 

 Gay Head section is one which in a measure serves to affirm the glacial 

 origin of this deposit. In my memoir on the Geology of Martha's Vineyard 

 in the 7th Annual Report of the Director of the U. S. Geological Survey, I 

 have called attention to the fact that a portion of the beds exhibited in the 

 Gay Head series are presumably of glacial origin, formed during an ice 

 epoch occurring in Tertiary time. This evidence was clearest in the case 

 of the conglomeratic beds which abound in certain portions of this section. 

 The facts in hand at the time when the above-mentioned report was pub- 

 lished were not sufficient to affirm this hypothesis. During the last summer 

 my assistant, Mr. J. B. Woodworth, was so fortunate as to discover in the 

 conglomerate exhibited just south of the depression known as the Devil's den 

 a fragment of ilmeuitic rock which certainly was derived from Iron hill, near 

 Cumberland, Rhode Island. The character of this material is such as to 

 make its origin quite unmistakable. The dense, fine-grained magnetic oxide 

 contains a large number of feldspathic crystals, giving the rock a very char- 

 acteristic expression. 



During the last glacial epoch a bowlder trail was formed from Iron hill 

 down the valley in which lies Narragansett bay and thence eastward to the 

 peninsula of Gay Head, whereon the fragments of the material are thinly 

 distributed. This fragment imbedded in the Gay Head section was discov- 

 ered at a point indicated in the section. There seems to be but little doubt 

 that it was actually imbedded iti the mass of the conglomeratic material. 

 Although found on the basset edge of the deposit there was no distinct coat- 

 ing of glacial drift above it, and it has the superficial color proper to the 

 deposit in which it is supposed to have belonged. Moreover, the surface of 

 the fragment is deeply pitted by decay in a manner exhibited by none of 

 the many thousand other fragments which were found in the trail formed 



