330 BULLETIIsr 103, UNITED STATES NATIONAL MUSEUM. 



2. The study of sediments in coral-reef areas has scarcely been initi- 

 ated. Accurate determination of the source of the constituents of 

 calcium-carbonate bottom-deposits should be made, the deposits should 

 be classified according to their constituents, at least the area occupied 

 by each kind of deposit should be ascertained as nearly as is practi- 

 cable, and an endeavor should be made to ascertaui the rates at 

 which the different kinds of sediments accumulate. The results from 

 investigations of this kind are of vital importance to geology, for 

 only by firmly basing our inductions on wide and accurate knowledge 

 of what is now happening in the ocean can we hope to make reliable 

 deductions concerning the origin of and the conditions under which 

 older sediments were formed. The quantitative evaluation of the 

 work done by the different agents cooperative in the production of 

 the different kinds of sediments should be an object constantly in 

 mind. Although this is essentially a new field of research, during 

 the past few years a number of investigators have notable achieve- 

 ments to their credit. 



3. Detailed studies of the general geology of tropical islands and con- 

 tinental areas adjacent to tropical and subtropical waters should be 

 undertaken wherever possible. These investigations should include 

 consideration of the stratigraphic and structural geology, the petrog- 

 raphy of both the igneous and sedimentary rocks, very detailed work 

 on the stratigraphic paleontology, and the physiography of the land 

 areas. We now know that, by combining knowledge gleaned from the 

 study of many relations, it is possible not only to recognize for an 

 area the succession of rocks, their age equivalents in other areas, and 

 their deformational history, but that it is also possible to ascertain 

 the successive physiographic stages and other physical conditions 

 throughout at least a considerable part of the history. The structural 

 relations of the successive formations, the nature of the contacts of 

 formations, and the character of the sediments, are among the criteria 

 to be used in making the latter kind of deductions. Of how many 

 tropical areas are there topographic maps on a scale of 1 : 62,500 or of 

 1 : 125,000? Many areas, where the geology is very comphcated, 

 should be mapped on a scale of at least 1 : 20,000. The very detailed 

 studies of a few carefully selected areas would supply keys for other 

 areas and thereby accelerate Vv'ork in other areas. Detailed work 

 of the kind suggested should be done in Antigua, St. Bartholomew, 

 St. Martin, and Anguilla, in the West Indies, for each of these islands 

 typifies certain phenomena that are critical in elucidating the history 

 of the West Indies, Central America, the southern United States, 

 and northern South America. 



4. Biogeographic investigations supply a basis for deductions regard- 

 ing former land connections and the dates of the separation of islands 

 that may have been parts of large land masses. 



