﻿I860.] 



JAMESON S.W. HIGHLANDS. 



143 



this view we should have the singular fact of an immense siicces- 

 sion of sedimentary strata developed here and nowhere else. This I 

 believe to have arisen from his having mistaken a trap-rock for an 

 aqueous sediment. 



Another feature of the case even still more singular, if we should, 

 with Macculloch, hold these greenstones to be merely highly meta- 

 morphosed aqueous sediments, would be the fact of immense fel- 

 spathic and hornblendic beds alternating with others remarkable 

 for the absence of both these ingredients, and all deposited from the 

 same sea. It is easily understood how beds of grit should alternate 

 with slate and schist ; for the one is the sand, the other the mud 

 of the old sea-bottom, separated by the action of gravity ; but it 

 would be difficult to comprehend how the action of sea-water could 

 have sifted so finely grains of felspar from those of quartz, their 

 specific gravity being alike. In the Silurian rocks of Wales and 

 elsewhere, beds supposed to consist of contemporaneous trap or 

 volcanic ash are interstratified with ordinary aqueous sediment ; 

 and it is quite intelligible that felspathic matter from an igneous 

 source might be ejected at intervals, so as to be thus interstratified 

 with quartz-sand derived from the erosion of different materials ; 

 but in such cases the beds of igneous matter have been distinguished 

 from the ordinary aqueous deposits with which they are associated, 

 by a name marking their proper origin. Whether, therefore, these 

 greenstone-rocks of Knapdale are of contemporaneous formation 

 with the strata beside them, or whether they have been subsequently 

 injected amongst them, they ought in my opinion to be clearly di- 

 stinguished from the grits and clay-slates, and not classed under the 

 head of a mere variety of these, as they have been by Macculloch. 

 I prefer, then, using the term bedded greenstone, as marking this 

 distinction and, at the same time, indicating the fact of their alter- 

 nation with the stratified layers, as well as conveying a more just 

 idea of their mineralogical features. 



I was unable to devote sufficient time for a thorough examination 

 of the district where these bedded greenstones occur, and would 

 recommend the locality to the attention of any geologist who may 

 have the opportunity, as likely to be well worth the labour of an 

 examination ; for it is very probable that here there may be green- 

 stones of different ages and various origin. I myself noticed some 

 vertical dykes of trap, of a blacker hue, which were evidently of a 

 later date, running in a N.W. direction, and cutting across both the 

 greenstone and grit, and causing alteration at the line of contact. 

 Two such may be seen in following up the course of the stream 

 that joins the Crinan Canal at Cairnbaan, and down which the tor- 

 rent descended when the reservoirs burst. 



The fact of veins of lead-, copper-, and iron-ores being met with 

 in several parts of this greenstone-traversed district, is a circum- 

 stance characteristic of igneous action. In the micaceous strata to 

 the south-west of Inverneil I saw a lode or vein of white quartz, a 

 foot or more thick, which in many places is very rich in galena, fre- 

 quently accompanied by sulphuret of iron and copper. This vein 



