406 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[May (>, 



of clay-slate, properly so called, arc such a very fine-grained mix- 

 ture of mica and quartz, that to the naked eye a rock of such a 

 nature might, and perhaps would, be looked upon by many as a 

 clay-slate — at all events it would be extremely analogous to some 

 clay- slates slightly altered by contact with granite. These portions 

 are not small beds interstratified with the very crystalline, but pass 

 into them irregularly along the plane of bedding, just as if the very 

 crystalline parts had been formed out of the fine-grained material 

 which here and there has remained in a comparatively unaltered con- 

 dition. 



From the facts thus briefly described we may, I think, unhesi- 

 tatingly draw the following general conclusions : — 



1. The existence of ripple-drift proves that the material from 

 which the schists were formed was mechanically deposited from 

 water. 



2. This material originally contained grains of sand, and was 

 probably a deposit of more or less pure sand and clay. 



3. Whatever may have been their original nature, the present 

 highly crystalline structure of the schists was developed after depo- 

 sition ; in some cases, indeed, after mechanical movements had pro- 

 duced complicated contortions and given rise to slaty cleavage. 



4. The bands of different minerals represent the planes of original 

 deposition, rendered very distinct by the alteration of thin strata 

 (which in unaltered rocks often differ more in chemical composition 

 than in appearance) into layers of minerals having entirely different 

 physical characters. 



3. On the Fossil Corals of the West Indian Islands. — Part I. 

 By P. Martin Duncan, M.B. Lond., F.G.S., &c 



[Plates XIII.-XVL] 



Contents. 



A. Preliminary Remarks. 



| II. Geology of Antigua, 



B. Enumeration of the Species, 



VI. Barbadoes. 

 VII. Trinidad. 

 VIII. Guadaloupe, St. Thomas, and 



I. Introduction. 



I. Antigua. 

 II. San Domingo. 



III. Jamaica. 



IV. Montserrat. 

 V. Barbuda. 



I. Antigua. 

 II. San Domingo. 

 III. Jamaica. 



St. Croix. 



C. Description of the Species. 



IV. Montserrat. 

 V. Barbuda. 

 VI. Barbadoes. 



D. General Observations on the Genera and Species. 



I. Antigua. 

 II. San Domingo. 

 III. Jamaica, 



IV. Barbadoes. 

 V. Guadaloupe, &c. 



E. Conclusion. 



