The Sterling Dolerite, 315 



May 8th.— Dr. Henry Woodward, F.R.S., President, 

 in the Chair. 



The following commnnieations were read : — 



1. ' The Stirling Dolerite.' By Horace W. Monckton, Esq., 

 F.L.S., F.G.S. 



The rock described in the paper forms a mass about 8 miles in 

 length, with an average width of about a mile ; it is intruded into 

 the lower part of the Carboniferous Limestone series. There is 

 little doubt that the Abbey Craig rock, N. of the Forth, is connected 

 with the Stirling rock ; and there is reason to think that the 

 igneous rocks of Cowden Hill and of the hills around Kilsyth are 

 outlying portions of the Stirling rock, being connected with it 

 underground. 



All these patches, as well as the main mass, are for the most part 

 composed of a more or less coarse-grained dolerite, the marginal 

 part always becoming finer-grained, whilst the actual edge has 

 apparently been a tachylyte now devitrified. 



The author gives the results of his macroscopic and microscopic 

 examination of the rocks from various parts of the mass. He 

 describes rocks from the centre, and also towards the bottom and 

 top of the main mass, including actual contact-specimens from 

 the bottom at Sauchie Craig and from the top at Sauchieburn 

 as well as contact-specimens from minor sheets ; and he infers 

 that the sequence is somewhat as follows (beginning from the 

 centre) : — 



(i) Coarse-grained ophitic dolerite, forming the greater part of 



the ma^s. 

 (ii) Fine-grained ophitic dolerite, say 10 to 20 feet from the 



margin, 

 (iii) Basalt with very little augite, and with rods of iron- oxide, 

 (iv) Basalt with porphyritic plagioclase-cryst als in a groundmass 



of microliths of plagioclasc and hairs and rods of iron 



oxide, having no augite. This occurs as near as | inch to 



the junction, and as far as 5 inches away from it. 

 (v) Basalt with porphyritic plagioclase in a grey groundmass, 



say -jJq to 1 inch from the margin, 

 (vi) Basalt with porphyritic plagioclase in a groundmass which 



is sometimes spherulitic ; about y^- inch thick on the 



average. 



2. 'Notes on some Railway Cuttings near Keswick.' By J. 

 Postlethwaite, Esq., F.G.S. 



Several cuttings have recently been made on the Cockermouth, 

 Keswick, and Penrith Railway, chiefly through drift, though some 



