41 



nodules, which upon fracture exhibit the changes of colour and ap- 

 pearance mentioned by Dr. MacCulloch, who first discovered this 

 mineral in the Isle of Rum. This substance has also been observed 

 by the author at Coaley-hill near Newcastle, in the steatitic or earthy 

 form, and but rarely crystallized. 



The reading was begun of a paper " On the Geological Relations 

 of the Secondary Strata in the Isle of Arran ;" — by the Rev. A. Sedg- 

 wick, V.P.G.S. F.R.S. Woodwardian Professor, and Roderick Impey 

 Murchison, Esq. Sec. G.S. F.R.S. F.L.S. &c. 



Feb. 1. — The reading of Professor Sedgwick and Mr. Murchison 's 

 paper, begun at the last meeting, was concluded. 



This paper consists of three divisions : 1st. A brief outline of the 

 general structure of the Isle of Arran. 2d. An account of the section 

 on the N.E. coast of the island. 3d. Concluding remarks explanatory 

 of the probable causes, and geological epochs of the several phe- 

 nomena. In the 1st division, the authors, considering that the sub- 

 ject has been amply elucidated by Jameson, MacCulloch, and Hen- 

 drick, confine themselves to such details as are necessary to make 

 their subsequent description intelligible. In the 2d part, the strata 

 on the N.E. coast are described in great detail, for the purpose of 

 comparison with the corresponding members of the English Series $ 

 from whence it appears, that a succession of formations, analogous to 

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

 are exhibited twice over, in an anticlinal section. 



The mineralogical centre of this section is at North Sannox, and 

 the lower red conglomerate is there seen in several situations, rising 

 to the height of about 1 000 feet above the sea. 1 . This formation is 

 supposed to be identified with the old red sandstone } from its lowest 

 members graduating into grauwacke ; from its containing concretionary 

 limestone not distinguishable from the cornstone of Herefordshire ; 

 and its being regularly overlaid by the carboniferous series. 2. The 

 middle deposit of the section is clearly referable to the carboniferous 

 series, by its mineralogical structure, by the organic remains in the 

 calcareous beds, which are identical with those of the mountain- 

 limestone ; by its containing seams of coal, which have been worked ; 

 and by the plants in the shale being of the same species with many 

 of those most abundant in the coal-measures of England. 3. The 

 superior sandstone and conglomerate are of enormous thickness, rising 

 into lofty and precipitous hills upon the coast. These are referred to 

 the new red sandstone, from their position and internal characters ; 

 and this classification is confirmed particularly by the structure of the 

 sandstone on the southern coasts of the island. This formation differs 

 however from the new red sandstone of England, not only in being 

 conformable to the beds on which it rests, but also by graduating into 

 the superior parts of the carboniferous order. 



In conclusion, the authors endeavour to show, that the great dis- 

 locations of the secondary deposits have been produced by an up- 

 heaving of the granite j and they state, in corroboration of this 



