326 Reports and Proceedings — 



II.— May 22, 1878.— Henry Clifton Sorby, Esq., F.E.S., President, 

 in the Chair. The following communications were read : — 



1. "On the Serpentine and Associated Igneous Eocks of the 

 Aryshire Coast." By Prof. T. G. Bonney, M.A., F.G.S., Professor 

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

 College, Cambridge. 



In a paper published in 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 Geolo- 

 gical 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 con- 

 clusions formed in the field have since been tested by microscopic 

 examination. 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 un- 

 doubtedly an intrusive rock, the evidence being abundant and re- 

 markably clear. One specimen can hardly be distinguished at sight 

 from the black serpentine of Cadwith (Lizard) ; the resemblance 

 also is most striking 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 hypersthenite is also intrusive. The author 

 foimd no hypersthene. There are two varieties — one a remarkable 

 rock, consisting mainly of large crystals of diallage, a gabbro ex- 

 tremely rich in this mineral and almost free from felspar ; and a 

 gabbro of later date, much resembling the ordinary gabbro of the 

 Lizard, the felspar being converted into a kind of saussurite, and 

 some of the diallage into hornblende. The " felspar-porphyries " 

 appeared to the author in the field to present all the characters of 

 true igneous rock, to be associated with tuffs, and to be unconform- 

 able with the above-described group of rocks. Microscopic examina- 

 tion placed their igneous character beyond doubt. There are also 

 some basalt-dykes of later date than the above. The author is 

 accordingly of opinion that the principal conclusions of the paper 

 referred to above ai^e not warranted by either stratigraphical or 

 lithological evidence. He considers it probable that the " felspar- 

 porphyry," like so much of that in Scotland, is of Old Eed Sandstone 

 age, and that the serpentine is of later date, but Palaeozoic. 



2. " On the Metamorphic and Overlying Eocks in the Neighbour- 

 hood of Loch Maree, Eoss-shire." By Henry Hicks, M.D., F.G.S. 



The rocks in the neighbourhood of Loch Maree have been de- 

 scribed by various authors, but chiefly and most recently in papers 

 communicated to the Geological Society by Prof. Nicol, of Aberdeen, 

 and by Sir E. Murchison and Prof. Geikie, of Edinburgh. The 

 views held by these authors in regard to the order of superposition of 

 the rocks are well known to be greatly at variance, not only as 



