40 Dr Davy ow the Use of the Microscope. 



composed minute crystals are to be seen — short slender 

 prisms, as of phosphate of lime ; and, chemically examined, 

 it is found to contain phosphate of lime, its chief ingredient 

 being the carbonate, with a trace of silica. 



The fertile soils of this very fertile island have been sup- 

 posed to be deficient in this last mentioned substance. When 

 subjected, however, to the microscope, the opinion is shewn 

 to be erroneous. In most of them silica is found in abun- 

 dance, either in the form of fine quartz sand, bearing marks 

 of being water-worn, or in excessively minute angular frag- 

 ments, probably of volcanic origin, or as the petrifying mat- 

 ter of infusoria. And chemical examination confirms this, 

 proving, in addition, that silica is largely present in combi- 

 nation with alumina. 



The sands of Barbadoes vary much in their nature, accord- 

 ing to the situation in which they are found. The sea-sand, 

 from two-thirds of the shore constituting the circumference 

 of the island, consists of comminuted shells, water- worn, with 

 very little siliceous or other matters, forming a valuable 

 material for the purpose of agriculture, although hitherto 

 little used. From the remaining one-third of the shore, viz., 

 from the north-east coast, the sand is a mixture of quartz, 

 in water-worn grains, and of comminuted shells, the former 

 preponderating. The shell-sand corresponds to one kind of 

 geological formation, the siliceous to another ; the one pecu- 

 liar to that part of the island, the greater portion of it con- 

 sisting of calcareous deposits abounding in marine organic 

 remains ; whilst the siliceous sand corresponds to the smaller 

 portion, formed of totally different deposits, partly chalk, con- 

 taining silicated infusoria, partly, and in larger proportion, 

 of clay, sand, and gravel, more or less cohering, with which 

 beds of coal are intermixed, the former seemingly the detritus 

 of primitive and transition rocks. Under the microscope, 

 using a low power, the appearance of these two kinds of sand 

 is distinctive. The shell-sand is merely diaphanous, whilst 

 the quartz-sand is transparent, not to mention other pecu- 

 liarities ; and in mixture, the grains of each are most easily 

 distinguislied, so that even without chemical examination, 

 on mere inspection, it may at once be pronounced which in- 



