ECONOMIC GEOLOGY. 285 



a considerable portion of the roads are repaired with this material, 

 and when subject to heavy trafiic become very uneven, from unequal 

 resistance. On adjacent portions of tlie lines of communication, Avhere 

 basalt, a rock both hard and tough, is used, a very even surface is 

 preserved. 



GYPSUM 



Occurs in beds of shale between the limestone, in a tubular form, 

 but only in small quantities. It exists in abundance near St. Joseph, 

 formino; a bed at least twenty feet thick, lyin<T unconformably on 

 highly inclined shales and calcareous slates. This deposit is very 

 pure, containing 93 per cent, sulphate of lime, (analysis furnished to 

 the Colonial Secretary,) and would probably more than suffice in quan- 

 tity for the wants of the colony. 



ALUM 



Is found efflorescing on cliffs of mica slate on the north of the Boca 

 Islands ; and near Macaripe, on the north coast of Trinidad. An abun- 

 dant supply of this article might be obtained, but the low price it 

 commands in commerce, and the limited demand for it in this colony, 

 would scarcely justify the outlay of capital for its manufacture. 



SULPHUR, 



In small quantities, is associated with alum and gypsum deposits^ 

 but does not require more than a mere notice of the fact. 



SLATES. 



The essential properties of good slates are a fine texture, compact- 

 ness, cohesion in one direction, resisting flexure, and at right angles 

 to this direction a highly fissile structure, depending more or less on 

 cleavage, and which should preserve a straight course in one and 

 the same place. For the advantageous working of a bed of slate it 

 must have a moderate width, and be tolerable free from quartz veins, 

 and other extraneous matter, which might destroy the regularity of 

 the structure. Although small pieces fulfilling all the requisites 

 may be obtained from the quarry at St. Ann's, generally the coarse- 

 ness of texture, the absence of transverse cohesion, the irregularity of 

 cleavage, and the interference of quartz veins, will prevent the appli- 

 cation of these slates to roofing purposes, but they may possess some 

 slight value in cases where the qualities just described can be partially 

 or wholly dispensed with. 



GOLD. 



. Reports have been circulated of the discovery of gold in the oxides 

 of iron, associated with quartz veins traversing clay slates at St. Ann's 

 quarry ; to ascertain the accuracy of such reports, four specimens of 



