.278 ANNALS NEW YORK ACADEMY OF SCIENCES 



complex. The stratigraphic series is made up of thousands of inter- 

 :fingeriiig alluvial fans, deltas, estuarine and littoral deposits, which have 

 been intruded by innumerable individual igneous bodies, all more or less 

 metamorphosed, faulted and folded. 



:;,, Across the northeastern portion of the area is a broad belt of rock be- 

 lieved to be Comanchic. The presence of Cladophyllia furcifera in a bed 

 of limestone and of fossil leaves in an adjacent hematite bed point, ac- 

 cording to Dr. Edward W. Berry and Dr. Frank H. Knowlton, to the 

 Gomanchic age of these beds. The basal portion consists mostly of 

 tuffs; the upper portion, of shales and a few limestones. Between this 

 belt of rock and the adjacent higher one there is a good evidence of a 

 period of folding and erosion. 



A conglomerate occurs at the base of the overlying belt of rocks. It 

 forms the backbone of the Sierra de Cayey, the principal mountain 

 range of Porto Eico. It is followed by alternating beds of shale and 

 limestone with a few beds of tuff and conglomerates. No fossils were 

 found in these beds, and it is assumed that they belong either to the 

 Gretacic or the Lower Eocenic system. They occur in a belt which curves 

 southward and eastward from the northwest corner to the southeast 

 corner. 



This is followed by a third belt, which is composed of a thick con- 

 glomerate at the base, followed by shales with several thick limestone 

 members. Jn these beds was found a pelecypod, Venericardia alticostata, 

 which is the typical index fossil for the upper Eocenic of the Gulf States. 

 A period of considerable uplift and prolonged erosion followed the de- 

 posit of these sediments. Upon the peneplained surface of the under- 

 lying complexly folded series of rocks thick limestone beds were laid 

 down. From this limestone Prof. Charles P. Berkey and Mr. D. E. 

 ^emmes gathered fossils, which Dr. W, II. Dall pronounced to be Upper 

 Oligocene in age. In the Coamo-Guayama district this limestone is rep- 

 resented by one small remnant of erosion. Its former great extent is 

 suggested by the superimposed drainage, which is now rapidly attaining 

 structural adjustment. Additional uplift in very recent time is shown 

 by river terrace deposits bearing fossils of recent age at elevations of 350 

 feet, above the sea. The volcanic centers which broke through the 

 Gretacic and Eocenic rocks are rather common features. All of these 

 have been worn down to their roots and are represented at present by 

 vents clogged with volcanic debris and surrounded by numerous in- 

 trusives and aureoles of hydrothermal alteration. It is thought that the 

 hot springs of this area are the dying out phases of volcanic activity. 



The paper was discussed by .Dr. Eeeds. 



