part 3] MINERALS TN CORAL-LIMESTONES OF BARBADOS. 171 



High-level Lovo-level 



Limestone. Limestone. 

 Insoluble in weak acid : 



Combined H,0 149 126 



Organic matter l 104 665 



Organic opaline Si0 2 29 107 



Quartz with chalcedonic Si0 2 ... 33 325 



Combined SiO., 818 691 



A1 2 0, 442 375 



Fe 2 0, 249 174 



FeO ' 20 47 



MnO 15 



Ti0 2 40 35 



CaO 12 30 



MgO 34 25 



K 2 24 20 



Na,0 11 37 



Zr0 2 trace 



P 2 0, 0-2 0-3 



Soluble in weak acid : 



Ca 3 2P0 4 280 201 



CaCO, 983,607 981,782 



MgC0 3 14,133 15,360 



1,000,000-2 1,000,000-3 



1 Containing N 2 5-8 10*? 



The proportions of the extraneous mineral fragments which I 

 was able to separate from the limestone in recognizable crystalline 

 and glassy forms were very small, the yields per kilogram of the 

 limestone being as follows : — 



Milligrams. 



High-level coral, Mount Misery 118 



High-level corals 45 



High-level beach-rock 105 



Low-level corals 560 



Low-level beach-rock 210 



The fact that such minute proportions can be readily isolated 

 from a limestone and more or less exhaustively examined, both 

 chemically and petrographically, is of interest. The present work 

 lias proved that during the long period in which the Barbados 

 coral-limestones were being deposited there were active volcanoes 

 in the West Indian Province, and indicates a mode of enquiry 

 which may give valuable results (in cases where beds of volcanic 

 tuffs are not present in limestones) in proving the existence of 

 contemporaneous volcanic activity. Possibly this study of the 

 extraneous mineral constituents of the Barbados coral-rocks may 

 lead to similar examinations being made of British and other 

 limestones, as additional to the excellent studies by Mr. E. B. 

 Wethered of the insoluble residues of the Carboniferous Lime- 

 stone Series at Clifton. 1 of the Inferior Oolite of the Cotteswold 



1 Q. J. G. S. vol. xliv (1888) p. 186. 



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