1871.] GEIKIE TERTIAKT TOIOANIC EOCXS. 279 



Sir P. Egeeton replied that there was no deficiency of pabulum 

 for any kind of fish in the sea represented by the Lias of Lyme 

 Regis. He also made some remarks on another somewhat similar 

 specimen in his own museum. The plate referred to bj Dr. Giinther, 

 he stated, was symmetrical, and not like the lateral plates on the 

 Sturgeon, which are unsymmetrical. He therefore thought it dorsal. 



2. On the Tektiaky Volcanic Rocks of the Bkitish Islands. By 

 Akchibald Geikie, Esq., F.R.S., F.G.S., Director of the Geological 

 Survey of Scotland, and Professor of Geology in the University of 

 Edinburgh. — First Paper. 



[Plate XIV.] 



In the present communication I propose to offer to the Society the 

 first of a series of papers descriptive of those latest of the British 

 volcanic rocks which intersect and overlie our Palaeozoic and Second- 

 ary formations, and which, from fossil evidence, are to be regarded 

 as of miocene, or at least of older Tertiary, date. Materials for this 

 purpose have been accumulating with me for some years past. In 

 bringing forward this fiirst instalment of them, I wish to preface the 

 subject with some general introductory remarks regarding the place 

 which the rocks seem to me to hold in British geology, and on the 

 nomenclature which I shall use in describing them. These remarks 

 will be followed by a detailed description of the first of a succession 

 of districts where the characteristic features of the rocks are well 

 displayed. Other typical districts wiU be described in future 

 memoirs. 



General Introduction. 



1. Area occupied by the Rocks. 



The rocks to which I propose to direct attention cover many 

 hundreds of square miles in the British Islands. They spread over 

 the north-east of Antrim, from Belfast to Loch Fojle, forming there 

 a great plateau or series of plateaux, with an area of fully 1200 

 square miles and an average thickness of 550 feet. From Ireland the 

 same rocks are prolonged northwards through the Inner Hebrides. 

 They form nearly the whole of the islands of Mull, Rum, Eigg, 

 Canna, and Muck. They cover fully three-fourths of Skye, and 

 extend even as far as the Shiant Isles. But far beyond our own 

 area they reappear with all their characteristic features in the Faroe 

 Islands, and again in the older volcanic tracts of Iceland. In 

 studying the volcanic phenomena which these rocks present to us, 

 therefore, we are not occupied with limited or local features, but 

 with the records of perhaps the most remarkable period in the 

 history of volcanic action in Europe— records which, in spite of th& 



