8 



ANNAL8 NEW YORK ACADEMY OF SCIENCES 



the aid of this transportation service and observations were made in suffi- 

 cient detail to judge the general character and structural relations of the 

 formations crossed. In addition to this kind of travel on the roads, short 

 trips were made on foot to examine features or outcrops of rock which 

 appeared to deserve investigation, and an occasional more extended trip 

 on horseback was taken to points in the interior. With these facilities 

 for travel, it was possible for both members of the party to give undivided 

 attention to geological observations. It was possible to stop and make 



Fig. 1. — Relief features characteristic of the interior ruiujcs of Porto IHco 



Photograph taken from the Ponce-Penuelas road at K-10, looking northward across 

 eroded formations of the older series to the main drainage divide. 



brief examinations along all the roads at hundreds of places, and, on 

 several of the roads crossing the island, sufficiently elaborate data were 

 secured to furnish a basis for geological cross-sections showing both relief 

 and structural features. A complete circuit of the island was made and 

 in addition it was crossed from north to south on three principal roads. 

 This, together with numerous side trips into the interior, permitted ob- 

 servations to be made on practically every formation of any considerable 

 consequence in the island. No point in the whole area is situated more 

 than seven miles from some road or other point of observation covered 

 by the party, and, even in those cases, except in the extreme southwest 



