362 On Metallic Minerals. 



It will be peixeived that the foregoing description of this 

 formation, contains much which is of a very local nature, 

 as far as regards opportunities of observation, and this must 

 be the case with all observations on the same subject for 

 many years to come, until the clearing of the country shall 

 open a better view of its geology and mineralogy to the 

 notice of the traveller. But 1 feel convinced, in the mean 

 time, that future examination will not discover any 

 characters in this formation essentially different fx'om those 

 here given, although facts of geological and commercial 

 interest, may doubtless be elicited. 



The older rock I have alluded to, as underlying this 

 limestone, is at all times one of these four — a sienite, or 

 greenstone, a sienitic granite, or sienitic gneiss. They 

 appear to pass one into the other, and to have a contem- 

 poraneous formation. As hornblende appears to be rarely 

 absent, without it be to give place to epidote, the presence 

 of which is very characteristic of these rocks, they may be 

 called amphibolic. As to the question, whether a genuine 

 granite occurs within the limits 1 have described, I am of 

 opinion that it does not, without it be as veins traversing 

 the other primary rocks. Mica is a rare ingredient in 

 them, and it appears to be in almost every case accompanied 

 by hornblende. As to the stratification of these rocks, 

 when most assuming that appearance, it is an ambiguous 

 case, whereas in the majority of instances, no signs of it 

 exist. Wherever the limestone prevails, the country is fltat 

 and tabular, rising sometimes in terraces, and always 



when first exposed to view, is of remarkably plumbagenous lustre, and being 

 marked with small pilastres, something like those on a stove, tinted columns 

 and flat surfaces, its appearance is at once singular and pleasing. Its lustre 

 however, does not continue without means being taken to preserve it, as 

 exposure to the air changes its colour to a dull brown. 



