60 ANNALS NEW YORK ACADEMY OF SCIENCES 



remains and which bear evidence of the continued depression favorable 

 for the growth of these accumulations for a considerable part of Tertiary 

 time. There is some suggestion in the relations shown in the eastern 

 portion of the island that this end was not wholly submerged and that 

 differential subsidence gave to this portion less prominent development 

 of the heavy, massive limestone beds. 



In later Tertiary time there was marked reemergence from the sea, 

 accompanied by warping, so that the later limestones and reefs were lifted 

 to very different elevations in different parts of tlie island margin. Since 

 that event, the whole has been again subjected to erosional attack of the 

 sea, and to wind work, with the result as now seen in the physical feat- 

 ures. The comparatively easily destroyed shales, marls and limestones 

 of the Tertiary series have been extensively removed, leaving only a 

 fringe of these formations along the north coast and a part of the dis- 

 tance along the south coast, and developing all of the topographic forms 

 characteristic of the erosion of emerged coastal deposits, together with 

 some very special forms due to the peculiar makeup and attitude of the 

 rocks themselves. 



Since this first emergence there have been minor oscillations also, the 

 record of which is observable in marginal terraces, deeply trenched flood- 

 plain deposits, and thoroughly indurated wind deposits of presumably 

 Pleistocene age. Apparently the latest movement has been one of slight 

 emergence. 



A summary, therefore, of the larger items in the geologic history in- 

 cludes the following: 



1) A long geologic period of volcanic activity, accompanied by marginal at- 

 tempts at assorting of fragmental and detrital material and organic accumu- 

 lation disturbed from time to time by renewed or extended igneous activity. 



2) A dying out of volcanic energy, greater stability of the mass with respect 

 to elevation and subsidence, and erosional attack continued long enough to re- 

 sult in extended planation and partial base leveling with final extensive sub- 

 mergence. 



3) The development of an unconformable overlying series of shales, reef 

 limestones and related deposits chiefly of organic origin, brought to an end by 

 final re-emergence. 



4) The development of present surface features under stream erosion and 

 marine marginal attack, with modifications arising from oscillation of level. 



The geologic column forming the basis of this outline, avoiding minor 

 details that are properly the subject of further study before specific state- 

 ment should be made, is as follows : 



