REVIEWS 821 
would destroy these shallow water forms, and since there would be no 
source for terrigenous material, the shells of pelagic life should have 
been the chief source of sediment. The problem is the same as that 
presented by the Niobrara chalk of the United States. It shows 
absence of terrigenous sediment rather than great depth of water. 
5. The next event in the history of Jamaica was the re-elevation of 
the island in the Oligocene period. The amount of elevation is esti- 
mated at 13,000 feet. If the preceding subsidence were less than stated 
above, the call for so great a rise would disappear. After this re-eleva- 
tion, the island is believed to have had a much larger area than now. 
The uplift was accompanied by a gentle folding of the rock, the 
folding having an east-west axis, and therefore making an angle with 
the axes of the older mountains, the trend of. which is northwest and 
southeast. With the general arching of this time there were many 
minor folds. It is believed to have been in connection with this ele- 
vation that the igneous intrusions of mid-Tertiary time were effected, 
and the higher terraces on the margins of the plateau developed. 
6. The next event was another subsidence, contracting the island to 
the back coast border. The depression is placed at about 3000 feet. It 
was at this time (as well as during the preceding interval of emergence) 
that the back coast border of the plateau was developed. During this 
minor submergence the Bowden formation (Miocene), reaching up to 
levels of 300 feet, was deposited. 
7. This subsidence was followed by an elevation. The Blue 
Mountain ridges and the plateau were elevated some 500 feet. ‘The 
borders must have been elevated much more, for the southern coast is 
believed to have been extended out to about the present 500-fathom 
line. This movement of elevation was less orogenic in its character 
than any of the preceding, and was followed by a period of erosion. 
During the pre-Bowden epoch of erosion the streams did not get their 
heads far back into the plateau, but developed great amphitheaters 
near the edge of the back coast border, while great basins were being 
developed in the interior. During the post-Bowden interval of erosion, 
the coast streams worked back, and drained out many of these interior 
basins. It was during this elevation that the middle terraces, of the 
back coast border—those at elevations of 200 to 700 feet—were 
developed. 
8. The next event was probably a late Pliocene subsidence of not 
more than 700 feet. This submerged the border of the island to the 
