Ill X. B. SHALEB — DEPOSITS OF EASTERN SfASSACHUSETTS. 



to reveal the position of the beds in the sections at < ray I Lead and elsewhere 

 in a far more satisfactory manner than they have been exhibited during the 

 pasl -i" years. Making avail of this favorable condition, 1 have been able, 

 through tin- assistance of my colleagues in the Burvey, to Becure a much 

 more accurate section of the Gay Head deposits than has previously been 

 obtained. The section given in the above mentioned reporl on the geology 

 of Martha".- Vineyard exhibits the beds Bhown at Gay Sead in the form of 

 an ordinary continuous monoclinal. This was the only interpretation which 

 was possible at the time this report was prepared. The section here pre- 

 sented show.- thai the former interpretation of tin- attitude of these beds 

 was much in error. They are not in fact generally in monoclinal attitude, 

 lnit are to a great extent singularly compressed, Bomewhat collapsed fold- 

 ings of the Bt rata. 



The taint traces of the-.' dislocations which were visible before the rubble 

 was cleared from the Gay Head escarpment by the great rain storm above 

 referred t«» were thought by me a- well a- other observers to be due to 

 irregular Bliding on the face of the escarpment as tin- detached masses from 

 the front made their way downward to thesea. The clearer view which has 

 recently hern obtained has shown tin- opinion untenable, for the foldings 

 are now traced hack to the portion of the cliff which i- 30 little disturbed 

 by slipping that the beds are Been in approximately their original attitudes. 

 It is now perfectly apparent that while some of the lesser folds may he due 

 to tie- irregular rate of the journey of the masses downward, the main dis- 

 locations arc clearly of an orogenic nature 



Long-continued work on the general surface of the bed rocks, the strata 



below the drift, in other part- of the island ha- also revealed the fact that 

 these deposits as a whole are not of monoclinal type, hut are apparently per- 

 vaded by similar great foldings. In the Gay Sead district the prevailing 

 Btrikes of the beds are Bhown on careful review to be substantially th< 



Stated in the preliminary report -that is, the axes of the lipid- are in a pre- 

 vailing northwest and southeast direction. There i-, however, a considerable 

 variety iii the attitude of the foldings, the range of strike being from N.20 

 E. toN. L2Q E. A- will he seen by the diagram in plate 9, the orogenic 

 forces have affected the whole of the section. No portion of the beds appar- 

 ently retain their original attitude. 



In the Chilmark and Tisbury districts, which lie east ami northeast of 



Head, beyond the deep depression occupied by Menemsha and Squib- 

 nocket ponds, a sudden change in the Btrike of the beds i- observed. For a 

 distance in a northeasterly direction of about !<• miles the beds have an al- 

 most invariable Btrike of northeast and southwest. Owing to the absence 

 of good sections, the foldings of the -t rata are not bo traceable as in the < la) 

 1 1 • .- 1 • 1 section. There appear to be at least two well-defined folds answering 



