﻿248 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



caverns, and the depth to which peat or swamp deposits that were 

 formed at or above sea level are submerged. Where there are recog- 

 nizable submerged wave-cut scarps, the depth of the base of the 

 scarp below sea level is nearly a measure of the amount of sub- 

 mergence ; the depth in the West Indies in some instances probably 

 exceeds the amount of submergence by about 6 fathoms. In the 

 case of islands that rise from a common platform and which biologic 

 and other data show were once parts of one land mass, the depth of 

 water on the common platform may be assumed to be an approxi- 

 mate measure of the amount of the rise of sea level with reference to 

 those islands. 



The criteria for determining the relative ages of elevated terraces 

 with reference to each other and for determinmg the amount of 

 deformation to which they have been subjected are as follows: (a) 

 Relative height; (b) relative amount of dissection; (c) relative degree 

 of inclination and direction of the slope of the terrace fiats ; (d) pres- 

 ence or absence of a succession of higher and lower terrace flats on 

 promontory tips and in places protected from vigorous marine cut- 

 ting; (e) stratigraphic relations of terrace deposits. 



Estimates of the endurance of the present relation of sea level 

 to strand line are based upon recognizing the stage of physiographic 

 development of the shore line. Among the important features to 

 be observed are the presence or absence and the character of sea 

 chffs bordering the shore; the amount of delta and aUuvial plain 

 building at the mouths of stream ways; the character of beaches, bars, 

 and spits; the nature and extent of the alluvial deposits back from 

 the shore; the profiles of valley sides; and the axial profiles of the 

 streams. 



CRITERIA FOR ASCERTAINING THE ROLE OF CORALS AS CONSTRUCTIONAL 



AGENTS. 



The failure correctly to evaluate corals as geologic agents has been 

 a defect of nearly all investigations of the so-caUed coral-reef prob- 

 lem; in fact, usually no attempt has been made to make such an 

 evaluation. This evaluation may be made in several ways, which 

 are as follows: (a) In studying fossil reefs exposed to view, the 

 relative proportion of coral to other constituents of the rock should 

 be estimated; (6) in studying marine bottom samples, percentage 

 estimates of the proportion of the different ingredients should be 

 made; (c) for submerged platforms on which reefs grow, the area 

 of the reefs should be compared with the total area of the platform, 

 an effort should be made to ascertain the nature of the rock under- 

 lying the sea floor between the reef and the shore, and the continuity 

 in outline of the platform should be compared with the extent and 

 position of the reefs; (d) knowledge of the growth rate of corals, 



