On Serpentine and associated Igneous Rocks of Ayrshire. 149 



ages are regarded by the author as great secular summers and 

 winters. 



3. " On the Distribution of Ice during the Glacial Period." By 

 T. E. Jamieson, Esq., E.G.S. 



The author believes that a study of the distribution of ice during 

 the Glacial period proves that the greatest accumulations of snow 

 took place in precisely those districts which are now characterized 

 by a very heavy rainfall ; and he pointed out how exactly this is in 

 accordance with the views of Prof. Tyndall as to the conditions most 

 favourable to the development of glaciers. In support of this con- 

 clusion he reviewed the phenomena presented by the most highly 

 glaciated districts of the British Islands, of Scandinavia, and Europe 

 generally, and of Asia and North America, and contended that in 

 every case his opinion is borne out, the districts which are now re- 

 markable for an excessive rainfall having been formerly centres of 

 dispersion for great systems of glaciers. The notion of a polar ice- 

 cap he held to be opposed to many well-known facts ; and he dis- 

 cussed the distribution of various forms of life during and since the 

 Glacial epoch, with the object of determining whether the drainage 

 of ice from the great polar basin was effected by means of the de- 

 pression of Davis's Straits or of Behring's Straits. The evidence 

 appeared to him to be in favour of the former channel. 



May 22. — Henry Clifton Sorby, Esq., E.R.S., President, in the 



Chair. 



The following communications were read : — 



1. " On the Serpentine and associated Igneous Rocks of the 

 Ayrshire Coast.?' By Prof. T. G. Bonney, M.A., E.G.S., Professor 

 of Geology at University College, London, and Eellow of St. John's 

 College, Cambridge. 



In a paper published Q. J. G. S. xxii. p. 513, Mr. J. Geikie states 

 that the rocks of this district are of sedimentary origin, a felspar- 

 porphyry being the " maximum stage of metamorphosis exhibited by 

 the felspathic rocks," and the diorite, hypersthenite, and serpentine 

 being all the result of metamorphism of bedded rocks. This view is also 

 asserted in the catalogue of the rocks collected by the Geological 

 Survey of Scotland. The author had seen specimens of rocks from 

 this district which so closely resembled some from the Lizard, that 

 he visited the Ayrshire coast in the summer of 1877. The conclu- 

 sions formed in the field have since been tested by microscopic exam- 

 ination. He finds that several, at least, of the group of " dioritic " 

 rocks are of igneous origin, and are dolerite and basalt, since they 

 contain augite, not hornblende. The serpentine is undoubtedly an 

 intrusive rock, the evidence being abundant and remarkably clear. 

 One specimen can hardly be distinguished at sight from the black 

 serpentine of Cadwith (Lizard) ; the resemblance also is most stri- 

 king when the rock is examined chemically and microscopically. 

 Examination of different varieties shows the serpentine to be, like 

 that of Cornwall, an altered olivine-enstatite rock. The rock called 



