166 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
beside the Caribbean shore of Colombia, and of other known high peaks 
like Orizaba and St. Elias adjacent to the Pacific shore lines of our ow! 
continent, 
So grand a subsidence and elevation as this must surely have left 
some record in the present submarine topography of the whole region, 
and we cannot contemplate maps of such phenomena without coming t? 
some very definite opinions which will be elucidated in Part V. Neither 
could the maximum of elevation have failed to expand the areas of the 
Antillean lands, and to unite many of the islands or even the mainlan 
together, especially had their geographic areas been greater then than 
now, which hypothesis seems tenable. 
The amplitude of the Bowden subsidence could hardly have exceeded; 
if it reached, 3,000 feet (500 fathoms). The data for this conclusion a? 
as follows : — The upper and lower limits of the deposition beds of this 
epoch are now practically visible. While they have, no doubt, bee" 
attenuated by erosion and their thickness has not been finally measured, 
they do not exceed 500 feet in thickness. The lithologie and sedimental 
character of the beds indicate a rapid gradation from off-shore to moderat? 
oceanie depths. The fundamental beds are gravels, much water wor 
embedded in marl, but contain no plant remains or other indications of 
ultra shallow deposition, although land shells do occur sparingly in them 
The fauna could not have lived at depths of over 500 fathoms. 
The presence of nearly four hundred species of Mollusca in a singl? 
horizon of one of the basement beds at first suggests immediate littoral 
conditions. Their mode of occurrence in the gravel, however, indicate? 
slightly deeper or off-shore conditions or origin, for had this gravel boe? 
near the beach line the delicate shells would have been ground al 
broken into breccia by wave action, and it is probable that they we! 
too deep to be influenced by any such action. The mollusca are such a8 
live at present at depths of Jess than 100 fathoms. The several species 
of Foraminifera, Bryozoa, and corals, especially the last, which are ^ 
simple non-reef-building species of the type which Pourtalés has me” 
tioned * as having probably lived at an average depth of 450 fathoms) 
indicate abyssal or continental deposition. These facts indicate that the 
basal Bowden beds, now exposed at sea level, were slightly below geh 
level at the beginning of the Bowden subsidence, and that the amou” 
of the depth must be subtracted from the total thickness of the Bowden 
to ascertain the true submergence, which could not have exceeded 500 
fathoms, 
1 Cited by Agassiz, “Three Cruises of the Blake,” Vol. 11. p. 19. 
