U.—On the Geological Relations of the Secondary Strata in the Isle of 



Arran. 



By the Rev. Adam SEDGWICK, V.P.G.S. F.R.S. 



(VVOODWARDIAN PROFESSOR IN THE UNIVERSITY OF CAMBRIDGE, &C.) 



And RODERICK JMPEY MURCHISON, Esq., Sec. G.S. F.R.S. F.L.S. &c. 



[Read January 18th, and February 1st, 1828.] 



§ 1, Introduction. 



DO much has been written on the physical structure of the Isle of Arran, 

 that an attempt to add our own observations to those which have been already 

 published may require some preliminary explanation*. 



After a careful examination, during- last summer, of the north-eastern shores 

 of the island, we thought that we discovered a sufficient proof of the existence, 

 in that region, of a succession of formations which are the representatives of 

 the old red sandstone, the carboniferous series, and the new red sandstone of 

 English geologists. 



If this conclusion be true, the evidence upon which it is founded (depend- 

 ing upon the observed superposition of the several beds, and the organic re- 

 mains contained in them) cannot be unimportant. For the details will not 

 only assist in completing- the natural history of Arran, but will connect its 

 structure with that of the neighbouring main land of Scotland. We hope, 

 also, that they will throw light upon the true relations of those masses of con- 

 glomerate which are spread out on both sides of the Murray Firth, which 

 form a well-defined mountain chain in the southern part of Caithness, and are 

 developed upon an enormous scale on the western coasts of Ross-shire and 

 Sutherland. The determination of the age of these great deposits appears, 

 after the facts published by one of the authors of this paper, to be the only 

 thing- wanted to fix the true epoch of all those interrupted fragments of 



* We more particularly allude to "The Mineralogy of the Scottish Isles," by Professor 

 Jameson ; "The Mineralogy, &c, &c. of the Island of Arran," by the Rev. James Ileadrick ; 

 and "A description of the Western Islands of Scotland," by Dr. MacCulloch. 



