Summary of Progress of the Geological Survey of Great Britain and the Museum of Practical Geology (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated.1898 Excerpt: ... trachytic tuffs, hornblende-andesites, and felsitic lavas are later Mr. Kynasthan the normal pyroxene-andesites. Hence we may conclude jte that in this district more acid material followed the eruption volcanic of the larger proportion of the characteristic intermediate lavas, rocks of Intercalation of ordinary sediments among the lava-flows are Lorne' by no means rare. As a rule they vary from two to six feet in thickness, and consist of red and purplish shales, with thin quartzose conglomerates. At the Bridge of Awe, however, as mentioned in the Survey Keport for 1896, a depth of from 40 to 50 feet of reddish and purple marls, shales, red and pale sandstones, and conglomerates is visible. These strata Mr. Kynaston has now ascertained to be interstratified with the andesites. Their more shaly portions might possibly yield fossils. Hitherto, however, they have proved unfossiliferous. Numerous sills of porphyrite traverse not only the andesites of Glen Nant, but also the much older sediments of the Kilchrenan area to the south and south-east. They can be traced to the Pass of Brander, and beyond into the altered rocks and granite of the western flanks of Ben Cruachan. The mineral composition and microscopic structure of these rocks have already been fully described. Their relationships and certain other points will be more fully discussed in later pages in connection with the Ben Cruachan granite. In previous Survey Reports the Ben Cruachan igneous rocks j" have been discussed together with the Dalradian series, although Etive it was recognised that they were younger than the plication and district (Mr. regional metamorphism of that series, and that they might Kynaston.) not improbably prove to belong to the volcanic history of the Lower Old Red Sandstone. T...