﻿328 Mr. D. Forbes' s Researches in 



cumulated in the beds of the rivers, and not been mined out of 

 the solid rock, the geological structure of the surrounding dis- 

 trict furnishes evidence as to its origin. A glance at the maps 

 published by Mr. Cunningham and Sir Roderick Murchison 

 shows that the country is composed of slates, schists, and other 

 highly metamorphosed rocks, now considered to be the represen- 

 tatives of the Lower Silurian formation, and further indicates that 

 these strata are in many places broken through and disturbed by 

 bosses and veins of eruptive granites. 



Mr. Hasweli informs me that his correspondents from Kildo- 

 nan write him that the main rock is slate traversed by granite, 

 and that china-clay is found along the banks of the burn, which 

 appears to have been produced from the decomposition of the 

 felspar in these granites ; so that it may be inferred that the 

 auriferous granite and the quartz and other dykes which invari- 

 ably are connected with its intrusion have been the cause of the 

 appearance of the gold itself, which most probably is of the same 

 geological age as in Cornwall, Wicklow, and many other parts of 

 both hemispheres. 



Babingtonite. 



This mineral species, which is essentially a silicate of iron and 

 lime, is of extremely rare occurrence, perfectly authentic speci- 

 mens having only been procured from its original locality (Aren- 

 dal in Norway); and there it is but very rarely met with, as small 

 crystals, associated with epidote and garnet in the iron mines. 

 It is said to have been found in quartz in the Shetland Islands, 

 and at Massachusetts on epidote ; but in the latter case Dana, 

 in the Supplement to the last edition of his ' Mineralogy/ p. 794, 

 states that the angular measurements are not identical. 



In 1854 I received from the late Mr. S. Blackwell a mineral 

 which had been discovered in a railway-cutting in Devonshire 

 in such quantities as to be used extensively as an iron ore, with 

 the request that I should assay it for iron. The sample in 

 question was found to contain 20*24 per cent, metallic iron along 

 with 48'26 per cent, silica. The mineral, which looked much 

 like a variety of hornblende, appeared to me to be worthy of 

 further examination; but as I shortly after started for my 

 foreign travels, I have been unable until lately to complete its 

 examination. 



The mineral itself occurs as an aggregate of groups of radia- 

 ting crystalline fibres which curve in towards their centres of 

 development, and possess a decided dark blackish-green colour; 

 its lustre is vitreous, and in very thin splinters it is trans- 

 lucent; it is somewhat dichroic, and gives green and brown 

 tints when examined by Haidinger's dichroiscope ; fracture im- 



