OF COE.VL-LIMESTO^^E FROM BARBADOS. 24 / 



cemented by pure crystalline calcite. The grains of this sand when 

 seen in section, are suhangular or rounded, and separated from 

 each other. Their size is about that of mustard seed or a little 

 smaller, their dimensions differing in various specimens but the 

 relative size of the grains in each specimen is remarkably even 

 Thev show the structure of coral, shell, nullipore, &c. ; m tact, 

 all the calcareous organisms noted in the last division, of which they 

 are the roUed fragments ; but they include also pieces ot consolidated 



"^ The localities from which they were obtained are as follows :— 

 Plumtree Gully, E. of Endeavour, 45 feet below surface 

 Plumtree Gully, E. of Endeavour, 30 feet below surface, b^O 



feet above sea-level. . ^ .v i- 



Ellis-Castle Well, at a depth of 130 feet from the surface. 



Cane Garden, from a tunnel 120 feet below the surface, and 500 

 feet above sea-level. 



Thicket Estate, from a shaft 87 feet from the surface. 



The Amphistegina-Tock (h) was obtained from Yaughans Estate, 



N. of Horse Hill. , ., . , ^ -ui 4.u 



The fact noted on p. 245, that organic calcite is less stable than 

 precipitated calcite, is nowhere shown better than m these rocks 

 (a) The specimens from Plumtree Gully are from a recognized 

 waterway in the coral-rock. It is here quite Porous from the 

 number of individual grains which have disappeared. All the cavities 

 correspond exactly with missing grains, and some have become 

 refilled with crvstalline calcite ; the outline of the original grain 

 being preserved'by a kind of edging of finely granular calcite, which 

 seems to surround each grain (see fig. 4, PI. IX.) 



(b) Only one specimen of this rock occurs. " It is from a block 

 of very hard white coral-rock, as large as a negro's cabin ly-mg on 

 the surface on Yaughan's Estate at a height of over /OO feet above 

 sea-level " A thin section shows that this rock consists mainly ot 

 foraminifera. The slide was sent to the late Dr. H. B. Brady, who 

 thus wrote of it :— " The prevailing foraminifer is Amphistegma 

 Lessonii (D'Orb.) ; it is a fine example of Amj^histegina-vock, the 

 shells now being mingled with coral-sand and the deposit formed 

 in shallow water, at not more than 8 fathoms and probably less 



than one." 



As in the above, the matrix is pure crystaUine calcite. 



Coral (?) mud, Codrington College. This is from a bed which 

 occurs at the base of the coral-rocks, between them and the Oceanic 

 series. The material is unconsolidated and is as fine as flour. Seen 

 under the microscope in glycerine, it appears to be made up exclu- 

 sively of minute calcitic crystals of a somewhat complex rhombo- 

 hedral shape, not all precisely alike in outline, but sufficiently so 



