212 G H. Morton — Geology of the Isle of Man. 



in a paper by the same author, published in the "Journal of the 

 Geological Society " for 1846, vol. ii. p. 317, there is a minute 

 description of the Carboniferous formation developed at the south 

 of the island, near Castleton, illustrated by maps and sections. Mr. 

 Cumming gives the order in which the subdivisions occur from the 

 top downwards as follows : — 



Posidonian Schists. 



Poolvash Limestone. 



Lower Limestone. 



Old Eed Conglomerate. 



He describes each of these subdivisions, the volcanic ash inter- 

 stratified with the Poolvash Limestone, and gives a list of 222 

 fossils found by him in the Carboniferous Limestone, showing the 

 range of each species. The Old Ked Conglomerate at the base of 

 the limestone is minutely described, and the area it covers is shown 

 on the geological maps. Several papers have since appeared on the 

 geology of the island, but one entitled, "A Sketch of the Geology of 

 the Isle of Man," by Mr. John Home, F.G.S., of the Geological Survey 

 of Scotland, 1 includes a concise account of the Carboniferous Lime- 

 stone, and confirms the arrangement of the subdivisions adopted 

 by Mr. Cumming ; indeed, no one, excepting Mr. Howorth, has 

 challenged the correctness of his conclusions, which have the appear- 

 ance of being the result of long-continued and careful observations. 



Mr. Howorth states that he spent three long days in examining the 

 deposits in the south of the island, but principally the Old Eed Con- 

 glomerate. That Mr. Cumming was "entirely erroneous," and that the 

 Old Red Conglomerate does not underlie the Carboniferous Limestone, 

 but is simply an overlying deposit of Boulder-clay, and remarks that 

 " A conglomerate consisting almost entirely of limestone boulders, 

 imbedded in a matrix of pulverized limestone, lying immediately in 

 contact with beds of limestone, cannot well by any process of 

 reasoning be made into an Old Eed Conglomerate." Mr. Howorth 

 searched carefully the various points where the deposit occurs at 

 Langness, but could find no evidence of it being overlain by the 

 limestone ; and at Cushnahavin he says he actually saw the latter 

 reposing on the underlying Silurian strata. He concludes the con- 

 glomerate to be a consolidated Boulder-clay, and that the trap-dykes 

 with the volcanic vent at Scarlet Point were posterior to the Con- 

 glomerate, and finally remarks that "We thus add another. remark- 

 able example to the list of volcanos active within the British seas in 

 Post-Tertiary times." 



During last summer, I, like Mr. Howorth, had three days in the 

 Isle of Man, which I devoted to the examination of the Carboniferous 

 Limestone and the Conglomerate at its base. Having read Mr. 

 Howorth's paper in the Geol. Magazine, I at once endeavoured to 

 ascertain the stratigraphical position of the Conglomerate, and I 

 found the difficulty of doing so somewhat over-estimated, although 

 the shore along the outcrop is only exposed at low water and soine- 



1 Trans. Edin. Geol. Soc, toI. ii. pt. 3, 1874. 



