EXTENT, DURATION, CHAKACTER, AND ORIGIN. 201 



I know, indeed, of no other field where rocks of an age so near the 

 present indicate such extreme compression. Their occurrence appear 

 to show a considerable renewal of the mountain-building forces in a 

 district which by its profound degradation seems to have been long 

 exempt from such accidents. It is an interesting question whether the 

 strains which created these folds have quite spent their force. So far as 

 the evidence from the fields in which they occur is concerned, it is 

 clearh^ to the effect that no movement has taken place since the pre- 

 glacial topography was developed. I have made a careful study of the 

 areas where the glacial drift is so thin that it does not hide the contours 

 and where the erosion effected by the ice seems to have been insignifi- 

 cant, and can find no trace of any postglacial deformations. The stresses, 

 though they were evidently ver}^ great, appear to have been effectively 

 discharged by the crumplings of the strata which they created. 



The question as to the nature of the orogenic movement which gave rise 

 to the folds of southeastern Massachusetts is interesting. On the main- 

 land, less than 20 miles away, the ancient gneisses and other highl}^ crys- 

 talline rocks afford the foundation for the relatively recent strata. This 

 fact, as well as the general character of the geology along this portion of 

 the Atlantic coast, makes it probable that the Cretaceous and the Tertiary 

 series of the islands rest on very massive deposits. We note also that the 

 glacial erosion which has been effected on the bottoms of Buzzards bay 

 and Vineyard sound has not brought into the Vineyard moraine materials 

 from any other than crystalline rocks, except relatively small fragments, 

 which we can trace to the Narragansett basin. It is difficult to conceive 

 that the foldings of the beds exhibited at Gay Head and elsewhere in 

 this district are the results of similar anticlinals and synclinals formed 

 in the massive rocks on which they lie or which must at least be not far 

 beneath them. 



Origin of the Movements. 



An exi)lanation of the method in whi(;h these foldings of Cretaceous and 

 Tertiary strata has been effected is perhaps indicated by the conditions 

 in the Richmond, Virginia, coal basin. In that field the Mesozoic rocks 

 have been thrown into sharply dislocated masses by the formation of 

 a synclinal, developed in the crystalline rocks on which they lie. Such 

 a trough in massive beds may be formed in large measure by faulting, 

 though the hypothesis of folding as well is not excluded. It is true that 

 in the Vineyard district there is no visible indication showing the sea- 

 ward side of such a trough as this suggestion calls for. It should, how- 

 ever, be observed that the crests of the ridges of crystalHne rocks which 

 are found along this shore decline rapidly seaward, so that the outer rim 



