358 Dr Davy's Account of Cole^s Cave, Barbadoe$. 



microscope, had the granular appearance of particles of clay, 

 with which were intermixed a few grains of excessively fine 

 quartzose sand. 



The tufa-like specimen, or that resembling porous sand- 

 stone, it has been already mentioned, consisted of crystalline 

 grains of carbonate of lime, and of a little clay or sand. With 

 this carbonate of lime a minute portion of phosphate of lime 

 was detected. The sand that remained undissolved by an 

 acid mixed with a little clay, consisted partly of water-worn 

 particles of quartz, and partly of particles like those of vol- 

 canic ashes, being angular with sharp edges ; — -such was the 

 appearance of both, as seen under the microscope with a high 

 power. 



Lastly, the clay was found to be very eottipounded, and to 

 contain carbonate of lime in small quantity, a little carbonate 

 of magnesia, a minute portion of alumine soluble in an acid, 

 and a minute portion of phosphate of lime, besides a portion 

 of sand, and a large proportion of clay not readily soluble in 

 dilute muriatic acid. Its compound nature was also indicated 

 by its fusibility before the blow-pipe. Amongst the speci- 

 mens I brought with me from the cavern, there were two 

 kinds I have not yet noticed. One was a fragment broken 

 from the wall of the cave : it consisted of incrustation of 

 carbonate of lime, coloured brown, and in part almost black* 

 Its colouring matter I found to be peroxide of magnesia, 

 mixed with some peroxide of iron. The other were small 

 masses, either spherical or oval, the largest not exceeding an 

 almond in size. They were numerous in one part of the bank 

 of the stream. When taken up they were soft and most 

 easily broken ; after exposure to the drier open air (the air 

 in the cavern tried by the moistened bulbed thermometer, 

 was found saturated with moisture) they increased in firm- 

 ness. Many of them when broken were found to have an 

 ochry nucleus, giving the idea that they might be embryo 

 concretions of clay ironstone, that in process of time the 

 proportion of oxide of iron might increase, and that ultimately 

 they might become included in a bed of clay. 



What are the influences which are to be drawn from the 



