140 
THE GEOLOGIST. 
The sum of Manx geology may be stated in a fe\A' 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 ]\Ir. Gumming calls the conglomerate of the Old Bed 
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 Pala^ontological evidence is not 
in favour of its being decidedly Old Red, for the fossils most abundant are 
Orthis Shar2oii and Favosites polyniorpha ; both these extinct forms being 
common to the Upper Silurian as well as the Devonian, and tlie 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. Tliese 
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, tliis 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 wdiich the clay-slates are thrown, it is 
exceedingly difficult to ascertain their thickness. It cannot be less, how- 
ever, the author thinks, than several thousand feet. The general strike of 
the beds is E.N.K., 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 
