94 Reports & Proceedings — Mineralogical Society. 



dolerite at Kettlestoun, composed of fragments of igneous and sedi- 

 mentary rocks cemented together by dolerite, and occupying a large 

 part of one face of the quarry. A peculiar spotted shale, due to 

 contact alteration, in the same quarry was also described. 



In connexion with the exposure of dolerite and overlying hornfels 

 at Auchinoon, it was stated that a quantitative analysis of the 

 alkalies in the dolerite showed a considerable falling off as the 

 margin was approached, and that while the hornfels in contact 

 showed nearly 7 per cent alkalies, no trace of lime was found in the 

 specimen analysed. 



2. " On a Section of the Wardie Shales, with Intrusions, exposed 

 in the Stank at Corstorphine ; and on the Draining of the Old Lochs 

 at Gogar and Corstorphine." By D. Tait. 



The main purpose of the communication was to record a hitherto 

 unrecorded section of the Wardie Shales in the Stank at the west end 

 of Dovecot Road, Corstorphine. The beds there consist of sandstone 

 and shales, dipping west at 20°. These are cut by two east and 

 west quartz dolerite dykes, which alter the shales in their vicinity. 

 The section is on the south side of the Middleton Hall fault, the 

 position of which is probably indicated by a spring of water situated 

 a few yards north of the locality. It was pointed out that this 

 section lies between Gogar Loch and Corstorphine Loch, both now 

 drained, and also midway between the buried river channels of the 

 Almond at Turnhouse and the Water of Leith at Roseburn. Both of 

 these channels are below sea-level at these points. It therefore 

 appears probable that the rocks in which this section was excavated 

 formed a watershed between them in pre-Glacial times. 



Photographs of a series of old maps, chronologically arranged, 

 were thrown on the screen to show the progress of draining of Gogar 

 Loch and Corstorphine Loch. An Act of Parliament shows us that 

 these draining operations were in progress in 166L Their final, 

 stage is recorded in the New Statistical Account, which says that 

 about 18.31 the Stank was widened and deepened. 



III. — Mineralogical Society. 



January/ 15, 1918. — W. Barlow, F.R.S., President, in the Chair. 



Dr. J. W. Evans : " Diagrams expressing the Composition of 

 a Rock." These diagrams are intended, like those of Michel Levy 

 and Miigge, to indicate at a glance the significance of the analysis of 

 a rock or complex mineral silicate. The molecular propoitions of the 

 constituents are determined in the usual manner, those of the ferrous 

 and magnesium oxides, however, being doubled. The silica is 

 represented by two rectangles placed side by side, the length of 

 each being half the molecular proportion of silica. In one of these 

 rectangles lengths equal to the molecular proportions of potash, soda, 

 and lime are measured off in succession, and in the other those of 

 alumina, iron oxide, and magnesia. Thus, the same space represents 

 both metallic oxide and silica, and so far as felspars, felspathoids, 

 or segirine are actually or potentialh- present, the monoxide and 

 sesquioxide they contain are with two molecules of silica represented 



