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THE GEOLOGIST. 



The sum of Manx geology may be stated in a few words. Along the 

 southern coast, on each side of Castletown, and having that place as a 

 centre, the Carboniferous limestone skirts the coast. It is separated into 

 two divisions by a thick bed of dark and thinly -laminated shales, many of 

 which are covered with Producti, etc. From underneath the lower beds of 

 limestone, what Mr. Curaming calls the conglomerate of the Old Eed 

 Sandstone, crops out. This bed, however, the author takes to be a sort of 

 passage from the Carboniferous downwards, rather than a representative 

 of the Devonian formation. Certainly the Palseontological evidence is not 

 in favour of its being decidedly Old Eed, for the fossils most abundant are 

 Orthis Sharpii and Favosites jpolymorjpha ; both these extinct forms being 

 common to the Upper Silurian as well as the Devonian, and the latter is 

 common both to them and the Carboniferous limestone. Striking off from 

 the coast inland, we find that these two deposits terminate at about two 

 miles ; and in going up the Silverburn we see them cropping out, first the 

 limestone and afterwards the red sandstone, both abutting against the 

 highly-inclined strata of the Cambrian beds. The area which the limestone 

 and red sandstone occupy is of a crescent form, having Poovlash on its 

 right horn and Santon-burn on its left : the whole distance being much dis- 

 turbed by outbursts of greenstone and trappean dykes. 



From Port le Maury, along the north-western coast, we come upon the 

 slate rocks, until we arrive at Peel, where a dun-coloured red sandstone 

 rests upon them ; the red sandstone rocks lying at a low angle. These 

 beds skirt the coast as far as the Point of Ayr, but do not extend into the 

 interior for a greater distance than four miles ; the farthest inland point to 

 which they extend being Kirkpatrick, where they are seen resting on the 

 still highly-inclined Cambrian strata. With the exception of these Palaeo- 

 zoic deposits, and the more recently accumulated beds of Pleistocene age, 

 the whole of the island is occupied by the Cambrian formation. 



The author, referring to an editorial note attached to an article of his 

 published in the ' Geologist ' magazine of September last, in which Mr. 

 Salter observes that we cannot tell whether these Manx clay-slates belong 

 to the Cambrian formation or not, until they have been properly surveyed, 

 says, — "At the most, this dictum is not attaching much value to the re- 

 searches of Strickland, Forbes, or Cumming ; and any one acquainted with 

 but the slightest knowledge of the Welsh Cambrians, on arriving at the 

 island would not fail to recognize in its highly-contorted beds the repre- 

 sentative of the former. I have no doubt whatever but that these Manx 

 beds belong to the true Cambrian system. So nearly are they allied in 

 mineral structure to those of Wales, that practical slate-dealers are unable 

 to tell the difference between the slates obtained from the recently opened 

 quarries of the island, and those obtained at Conway. And not only in 

 the mineralogical appearance of the beds is there a similarity, but also in 

 the organic remains, few though they be, which the Manx beds have 

 yielded. At the same time we have seen that the supposed representative 

 of the Old Eed Sandstone, as well as the overlying Carboniferous lime- 

 stone, both abut and rest on the clay-slates themselves." 



Owing to the contortions into which the clay-slates are thrown, it is 

 exceedingly difficult to ascertain their thickness. It cannot be less, how- 

 ever, (he author thinks, than several thousand feet. The general strike of 

 the beds is E.N.E., the strata running in parallel mountain-ridges, of 

 which the principal one is that passing through Slieanwhallin and North 

 Barrule. The valleys between these principal ridges are mostly formed 

 by the synclinal depressions of the strata — from one end to the other — the 

 whole tract of the Cambrians being highly contorted, and broken up by 



