BERKEY, GEOLOGICAL BECONNOISSANCE OF PORTO RICO 65 



metals as well as a number of non-metallic products. But in no case is 

 tlie real value, or the probable extent or the geological relation, known 

 sufficiently well at the present time to serve as a basis for a discussion. 

 This should be one of the first undertakings of this survey, both because 

 of the fact that its value is fully appreciated by the people of Porto Eico 

 and because its conclusions do not materially depend upon the other in- 

 vestigations or mapping progress. 



PETROGRAPHY 



On account of the great number of igneous rock occurrences and the 

 very great variety that is certain to be shown in quality and minor 

 petrographic character, and because of the considerable range in compo- 

 sition already known to characterize the intnisives, there would seem to 

 be an ample and promising field in this line for a special investigation. 

 Tt is possible that some genetic relationship is exhibited in the distribu- 

 tion of these variations and that a thorough comprehensive study would 

 throw some light on the more obscure problems connected with the gen- 

 esis of igneous rocks. This is a problem that can be taken up at any 

 time, and that need not be regarded as dependent upon special district 

 studies, although it is evident that the finishing of work on certain dis- 

 tricts would facilitate a study of this kind. 



PHYSIOGRAPHY 



Enough is known of the physiographic features and their meaning to 

 appreciate that a great deal of the detail of the later geologic history of 

 the island is more or less intimately bound up in the physiographic de- 

 velopment. The broader or larger physiographic featiires have already 

 been suggested, but there are certainly many details, some of which may 

 well be of much significance in understanding the geologic history, which 

 will require the special attention of a trained physiographer. Porto Eico 

 is a unit of geologic history, of geologic structure and of physiographic 

 form. Each is of sufficient complexity and unity to be made independent 

 subjects of investigation. 



THERMAL WATERS 



The hot springs in the vicinity of Coamo Springs suggest from their 

 situation and reported composition the possibility of being representa- 

 tives of juvenile waters. It is believed that a study, planned especially 

 to investigate the origin and character of these waters, together with such 

 others as may exist, would be a very suitable special investigation. On 



