1897.] NEW YORK ACADEMY OF SCIENCES. 123 



this period ; certainh'' it was interrupted sufficiently to admit of 

 leveling projecting islands. The steep walls of Harrington 

 sound tell somewhat of undercutting and of falling cliffs, but not 

 until within four fathoms of the surface is the broad bench 

 reached, which tells of slow change and long-continued under- 

 cutting on approximately one plane. This four-fathom line is 

 important also in Castle harbor, the lagoon and the sounds be- 

 yond Hamilton harbor. The conditions within Castle harbor 

 and the lagoon show also that very near the end of the period 

 the subsidence was interrupted for a long time, long enough to 

 permit the leveling of broad areas, which now are flats, six 

 inches to two feet below tide. There is no reason to suppose 

 that the land of those areas had less altitude than the islets re- 

 maining on the ocean side of Castle harbor or the North Rock, 

 that relic of the great reef's land. The same general condition 

 prevails along the south shore, where the outlying ridges were 

 planed off" at a little below tide, so as to form the so-called 

 "bounding reef." 



I am led to the following conclusions respecting the succession 

 of events : 



First. The limestone or " base rock " of the islands was 

 formed by accumulation of dune sand. During a prolonged 

 period of quiet this rock underwent severe erosion, both surface 

 and subterranean ; the collapsing of cavern roofs caused great 

 " sinks," some of which, no doubt, still exist as such, though to 

 distinguish them from those of later origin would be difficult. 



Second. A period of subsidence followed, during which the 

 land sank one hundred and twenty feet or more ; marine deposits 

 encroached upon the land, extending inland through valleys, 

 thus giving beach rock at widely separated localities and in 

 somewhat anomalous positions. 



Third. Succeeding this was a period of quiet, during which 

 the sandstone was formed, as the limestone had been, by ac- 

 cumulation of dune sand, and the great sinks were filled up as 

 the basins of Castle harbor are now filling. 



Fourth. A period of elevation followed, during which the land 

 must have risen to at least its former level. The old subter- 

 ranean drainage systems were re-established in many instances 

 and former depressions cleaned out; while new systems may 

 have been formed, causing new groups of depressions. 



Fifth. This was succeeded by a period of subsidence, during 

 which the land sank to very nearly the same position as at the 

 maximum of subsidence in the former period, the highest marine 

 beds being now only a few feet above the water's edge. The 

 more imjjortant bodies of water began in the deeper depressions 



