0^ THE GEOLOGY OE BARBADOS. 177 



grey crystalline limestones, varying in depth of tint. In thin 

 seclions that which may be called the matrix is seen to be granular 

 crystalline calcite ; the texture, ho^vever, varies, some parts being 

 coarser than others, and in all there are ramifying veins and 

 patches of clear crystalline calcite. These veins not unfrequently 

 contain clearly defined foraminifera and radiolaria, as well as small 

 accumulations of minute, angular mineral chips such as are met 

 with sparingly throughout the rock. 



These rocks appear to be earths which have been rendered 

 crystalline by the infiltration of calcite. The two former were 

 originally calcareo-siliceous earths, for both foraminifera and radio- 

 laria are still discernible in the less altered parts. The last 

 must have been almost entirely siliceous, for no foraminifera 

 were noted, and about one third of the slice examined consists 

 of inorganic material. The slide was therefore sent to Miss Raisin, 

 who found the mineral fragments were chiefly pumice and felspai-, 

 with a few pieces of brown glass, and- one or two grains which 

 might possibly be quartz. There is one piece of vesicular pumice, 

 infiltrated with calcite, which is of unusual size (about 1 mm. in 

 length) ; also a large clear felspar which has a twinned structure, 

 and contains negative crystals elongated along the planes of the 

 felspar. 



The minuter elements of the Barbados Rocks. — 

 Mr. Hill contributes the following remarks : — When the finest 

 material of the Barbados earths is examined under the micro- 

 scope with high powers, say yL_inch objective, much of it can 

 be recognized as foraminiferal or radiolarian debris, but much also 

 consists of particles derived apparently from neither of these 

 sources, and a proportion is in so fine a state of subdivision that it 

 affords no clue to its derivation. 



(a) Calcareous Earths. — By breaking up a small fragment of the 

 most calcareous earths^ e. g. the Canefield Chalk, in water, that 

 which sinks readily to the bottom is chiefly foraminiferal debris, 

 but 50 per cent, of that which remains suspended, after half a 

 minute has elapsed, will be found to consist of bodies which answer 

 to the descriptions given by Prof. Huxley,^ Dr. Sorby,^ and others 

 of the coccoliths and crystalloids of the English Chalk and Atlantic 

 oozes, and a large part of the remainder may be referred to frag- 

 ments of such bodies. There are two types — oval and stellate, with 

 some variety in size and ornamentation. 



The oval forms (see next page, figs. 7, 8, and 9) are larger, but 

 agree generally with the description given of the coccoliths of the 

 English Chalk and Atlantic ooze. They are usually convex in shape, 

 and many have the duplicate structure described by Prof. Huxley as 

 somewhat like a shirt-stud. They consist of a central disc, which 

 is sometimes granular in appearance and sometimes in the larger 

 forms ornamented by an irregularly shaped cross (fig. 7), but more 



^ Huxley, 'Deep-sea Soundings in the N. Atlantic Ocean made in H.M.S. 

 Cyclops,' Appendix to Admiralty Eeport, 1858. 



'^ Sorby, 'On the Organic Origin of tbe so-called Crystalloids of the Chalk,' 

 Ann. & Mag. Nat. Hist. vol. Tiii. (18G1) p. 193. 



