BERKEY, GEOLOGICAL RECONNOISSANCE OF PORTO RICO 61 



Recent alluvial deposits. 



Submergence with flood-plain deposits. 

 Younger Series. 



San Juan dune sands (Pleistocene). 

 Submergence with terrace cutting. 

 Post-Arecibo emergence and erosion. 

 Organic limestones, marls etc. (Mid-Tertiary). 

 Arecibo reef limestones (Oligocene). 

 Lares shales etc. (Eocene ?). 

 Marked unconformity. 

 Older Series. 



Interbedded limestones, tuffs and shales etc. (Cretaceous), Coamo 

 tuff -limestone, Trujillo Alto limestone, Aibonito conglomerates and shales 

 with many intrusives. 



Interbedded foraminiferal shales and ash shales with tuffs, cut by 

 many intrusives (Early Cretaceous ?), Fajardo shales, Mayaguez shales, 

 Barranquitas shaly limestones. Sierra de Cayey tuffs, Comerio consoli- 

 dated ash beds and tuffs, etc. 



Future Peoblems 



One of the objects of this exploratory study was to discover and define 

 the problems that should be investigated by this organization. It is not 

 supposed, in enumerating this list, that these cover every possible subject 

 of special study, but they do indicate the fields in which there is promise 

 of immediate and valuable scientific returns, and at the same time will 

 add to the fund of usable information to be put within reach of the people 

 of Porto Eico. 



BASE MAP 



One of the fundamental things as a basis for all sorts of detailed geo- 

 logic work is a good contour map. The whole island ought to be mapped 

 in the same manner as is done in the United States, using the same 

 quadrangle system. On account of the density of population, the com- 

 plexity of structure and relief and the variety of agricultural uses of the 

 soil, the scale should be approximately one mile to the inch, or 1 : 62500, 

 so that these maps could be used as base maps for all sorts of special 

 purposes. 



The maps now available are chiefly those of the Interior Department 

 of Porto Eico, made to illustrate the various reports of the department 

 and representing the progress of public works such as railways, telegraph 

 and telephone lines and highways. On account of the care with which 

 the different classes of roads have been shown, and the general accuracy 

 of locations, these maps are especially useful in the present investiga- 

 tions. One of the most useful is a map of the Bureau of Public Works 



