174 Revieics — Br. Spencer — The Antiliean Continent. 



Particulars are given of some of the channels which cross the 

 Blake Plateau ; some of them are traceable for 200 or 300 miles 

 and reach a depth of 10,000 feet before they are lost in the si;b- 

 oceanic embayments. The deep troughs which furrow the Bahama 

 Plateau present the same features, and a study of the United States 

 hydrographic charts of the Gulf of Mexico exhibits a similar 

 state of things — an upper continental shelf to about 600 feet, and 

 then a slope, in some places gradual, in others steep, down to depths 

 of 9000 to 10,000 feet. Both shelf and slopes are traversed by 

 valleys, the floors of which are often several hundred feet below the 

 plateaux on each side, and these valleys seem to be prolongations 

 of those by which the modern continent is drained. 



All these features are shown on the map which accompanies the 

 paper, and below the Straits of Florida a broad submerged valley 

 is seen draining icestward into the Gulf of Mexico, not into the 

 Atlantic. The Sea of Honduras and the Caribbean Sea are basins 

 comparable to the Gulf of Mexico, but the floor of the former seems 

 to have been deformed by late erogenic disturbances which have 

 produced long depressions parallel to the mountain ranges of Cuba 

 and Jamaica. 



Dr. Spencer's conclusion from all the evidence is, that after 

 making all allowance for possible foldings the northern side of the 

 Gulf of Mexico has been sunk not less than 8000 feet, and that the 

 south-east part of North America, together with the Greater Antilles, 

 has been depressed for 10,000 or 12,000 feet; that before this 

 depression the two Americas were united along the West Indian 

 ridge, and that the deep basins of the Caribbean, the Honduras Sea, 

 and the Gulf of Mexico were broad plains through which rivers ran 

 li'eHiicard into the Pacific Ocean. He believes that these conditions 

 lasted till a comparatively recent date and that when the barrier of 

 Central America was raised the Antiliean basins sank. 



He next endeavours to determine the probable dates of elevation 

 and subsidence, a study which of course involves a correlation 

 of the various formations that have been described by diiferent 

 authors in the several islands of the West Indies. This part of the 

 essay is not quite so satisfactory, partly because too little is yet 

 known of the geology of the West Indies, and partly because 

 Dr. Spencer's own observations in Cuba are not yet published, so 

 that we are here presented with some of his conclusions without 

 all the data on which they are founded. His reading of Antiliean 

 history is as follows : — 



In Eocene times there were islands round which shallow-water 

 deposits were formed, but no continental connection. The Miocene 

 period was one of deep subsidence, and deposits, largely of deep- 

 water origin, were accumulated to a thickness in some places of 

 more than 2000 feet, the Pacific and Atlantic being broadly united. 

 During Pliocene times came a great upheaval, and the sea floor was 

 raised to elevations of from 8,000 to 12,000 feet above the present 

 sea-level. The Antiliean region was united to both Americas, and 

 the drainage was westward into the Pacific. 



