Geological Society of London. 183 



undergo remarkable cliauges as we pass from the superficial to the 

 central portions of these intrusive rock-masses. The most important 

 of these changes is that for which the author proposed the name 

 '* schillerization." It consists in the development of microscopic 

 enclosures, in the form of plates and rods, along certain planes 

 within the crystal, giving rise to metallic reflections or a play of 

 colour. The felspars, pyroxenes, and olivines are all found to be 

 afi'ected in this way when they have formed the deepest parts of 

 these volcanic cones. In this way common augite is seen at gradu- 

 ally increasing depths, passing into the deep brown variety known 

 as pseudo-hypersthene. The last-mentioned substance presents a 

 curious " mimicry " of true hypersthene and paulite, which is the 

 schillerized form of a ferriferous enstatite. 



The Tertiary peridotites present many variations, not only in their 

 structure, but also in their mineralogical constitution. Among them 

 occur examples of the rocks which have received the names of 

 dunite, picrite, and Iherzolite, with some curious types composed of 

 felspar and olivine. 



Among the older peridotites of Scotland a new and very interest- 

 ing type is described from near Loch Sc3'e in Caithness. It appears 

 to have been originally a raica-picrite, but the whole of the original 

 minerals have been converted into paramorphs, firstly by schilleriza- 

 tion and subsequently by amphibolization and serpentinization. 



In conclusion, it was pointed out that the discrimination between 

 the effects of the changes described as schillerization and those 

 known as uralitization, amphibolization, serpentinization, and 

 kaolinization is of the utmost importance, not only to the petro- 

 grapher, but to the mineralogist. 



2. " Boulders wedged in the Falls of the Cynfael, Ffestiniog." By 

 T. Mellard Eeade, Esq. 



This paper briefly described certain phenomena of stream-denu- 

 dation observed in the bed of the Cj^nfael, which has cut a deep, 

 channel through the Lingula Flags, the course of the channel being 

 mainly dependent on the jointing of the rock. In one spot the 

 upper beds at the top of the gorge have slid upon the lower along 

 their dip, about 10° to north by east, so as to project over the stream 

 like a corbel ; and advantage has been taken of this to form a bridge 

 by means of a slab of rock laid from the projecting mass to the top 

 of the opposite bank. At another point several very large boulders 

 are stuck fast in the channel, and the stream flows beneath them. 

 The boulders coukl not possibly have been carried down the existing 

 gorge, and they had not, the author believed, fallen from above. He 

 suggested that they might have been carried down by the aid of ice, 

 probably in the glacial period, when the stream ran in a wider 

 channel, and that they have been polished by the action of the water. 



III. — Annual General Meeting, February 20, 1885. — Prof. 

 T. G. Bonney, D.Sc, LL.D., F.R.S., President, in the Chair. 



The Secretaries read the Reports of the Council and of the Library 

 and Museum Committee for the year 1884. The Council's Report 



