1897.] NEW YORK ACADEMY OF SCIENCES. 121 



Prior to subsidence, the extreme altitude of the old limestone 

 surface was little more than one hundred and seventy feet, as- 

 suming subsidence to tlie twent^'-fathom line, while the general 

 average of the surface, as shown by distribution of the sand- 

 stone and its relation to bosses of the limestone, must have been 

 much lower. It seems difficult to find material enough during 

 the subsidence as marked out by the old beach deposit. But be 

 that as it may, the helix-hed and its distribution show that during 

 subsidence the sandstone accumulated very slowly and that rapid 

 accumulation did not begin, as has been stated already more 

 than once, until after subsidence had practical!}' ceased. If sub- 

 sidence had been continuous, the Devonshire bay deposit would 

 have been covered with "coral crust" as in the Ireland island 

 excavation and not with sandstone as it is. The distribution of 

 sandstone on the islands of Castle harbor makes more than prob- 

 able that it covered all the " flats " or " bounding reef" along 

 the south shore, which are merely a continuation of those islands ; 

 so that that rock must have reached seaward a full mile be3'ond 

 the marine deposit at the head of the Devonshire creek. 



It is difficult to conceive of the accumulation as materially 

 aided b}- elevation succeeding depression. The bringing of new 

 area into the sphere of wave action is somewhat indefinite ; espe- 

 cially so because a long continued and evidently' gradual subsi- 

 dence had been bringing new area within the sphere of wave 

 action without aiding accumulation ver}' much — as appears from 

 the petty thickness of the helix-hed. It is, of course, possible 

 that sands made during subsidence and carried seaward might 

 be exposed again by elevation. 



To the writer it seems altogether most probable that the sand- 

 stone, as a mass, accumulated during a period of quiet or of 

 elevation so slow as to be without material influence upon forma- 

 tion of the rock. The surface of the limestone had become, prior 

 to subsidence, much like that of the land now; so that during 

 subsidence sinks near the shore were converted into ponds, and 

 the ridges separating them became islands, while valleys, through 

 which streams had flowed, became creeks, in which accumulated 

 marine deposits as at Devonshire bay and the other localities, 

 whence seaward channels can be traced on the map. The ma- 

 terial obtained by planing off the ridges during a period of 

 quiet might form the mass of sandstone in the central part of the 

 area. It is possible that during slow elevation the lower por- 

 tions of the planed-off ridges might be cut ofl" by the waves, so 

 as to supply some material for sandstone at the easterly side. 

 At the same time the knowledge available now seems insufficient 

 to justify any positive conclusions respecting conditions prevail- 



