161 



PROF. J. B. HARRISON OX EXTRANEOUS [vol. lXXV„ 



the whole, of that from the low-level corals and beach-rock is 

 clastic and derived from the quartz-sand beds of the Scotland 

 Series exposed in the eastern section of the island. The analyses 

 have, therefore, been recalculated to eliminate the ' quartz.' The- 

 results of this are as follows : — 



Percentage Composition of the Mineral and Glass 

 Constituents other than Quartz. 



1. 2. 3. 



4. 5. 



Combined Si0 3 ! 72'10 7537 



AloOy i 660 11-25 



72-43 



14-42 



nil 



7-69 



•96 



•64 



1-92 



1-28 



•64 



60-22 63-04 

 16-51 1 18-60 

 3-81 i nil 

 2-43 ! 4-06 ! 

 •27 ! -53 

 5-53 178 i 

 1-55 3-09 

 203 i 2-11 

 7-65 : 6-71 



Fe"() y ' nil nil 



Ft() 5-07 764 



Ti0 2 ^ nil nil 



CaO 1 9-64 -85 



MgO 1 4-06 1-70 



K«0 2-03 1-06 



NaoO -51 2'12 





Totals j 100-01 99-99 



99-98 



100-00 99-92 









These analyses of the extraneous mineral constituents of the- 

 Barbados limestones indicate that, in addition to ferruginous 

 kaolin which may have been derived from extremely finely-divided 

 clay held in suspension, or even in colloidal solution, in the ocean- 

 waters, they contain minerals of igneous origin. 



Before the detailed microscopical examinations were made, the 

 heavy minerals, including hornblende and pyroxene, were separated 

 from the lighter by the use of a Sonstadt solution of sp. gr. 2*90. 

 The fragments of the lighter minerals were approximately separated 

 into basic plagioclase, quartz, sanidine, and glass by bromoform 

 suitably diluted with 98 per cent, alcohol. Owing to the minute 

 size of the fragments and to the fact that many of them contained 

 inclusions of other minerals or of gas-bubbles, it was not feasible 

 to make these separations quantitatively. 



I now proceed to describe the results of the microscopical 

 examination of the residua. 



The residua from the calcified or reerystallized coral of Mount 

 Misery, in addition to kaolin and abundant flakes of limonite and 

 grains of haematite, contain only low proportions of crystalline and 

 glassy minerals. With the exception of some minute but perfect 

 crystals of hypersthene, the minerals present are in sharply-angular 

 fragments, those of glass consisting of conchoidal, very sharply- 

 edged flakes and splinters. Very few of the fragments of felspar 

 are of plagioclase, most of them being glassy sanidine. There are 

 a few flakes of dark-brown biotite and some angular fragments of 

 green and of colourless augite, and of a dark-green hornblende. 

 A small crystal of zircon, and some minute crystalline fragments 



