Vol. 56.] EAKTH-MOVEMENT IK THE ISLE OF MAN. 21 



incipient folds, the crests of which have been pinched off and carried 

 forward along the minor thrust-planes between separate blocks of 

 the overlying disorganized mass. 



Essentially the whole structure is a small-scale reproduction of that 

 well-known feature in mountain-building — the broken and over- 

 thrust anticline. The peculiarity of the present instance is that the 

 development of the structure appears to have been determined 

 mainly by the lithological contrast of the rocks at a strictly local 

 focus. It is highly probable that local disturbances of this type 

 will be found wherever the same conditions prevail, though such 

 opportunity for demonstrating them as is afforded by the magnificent 

 coast-exposure of the Isle of Man must necessarily be rare. I may 

 be permitted to state that four years ago, when seekiug for structures 

 analogous to the crush -conglomerates of the Manx Slate in the Lake 

 District, my attention was directed by Mr. Marr and Mr. Harker to 

 sections in the Borrowdale Yolcanic Series under the Sty-Head Pass, 

 where they had noticed brecciation of the bedded ash. On ex- 

 amining these sections I came to the conclusion that the structures 

 were not of the type of which I was in search ; but now, on reading 

 my notes made at that time, I recognize features closely similar to 

 those presented by the Manx Carboniferous bedded tuffs, though the 

 mineral condition of the rocks is quite dissimilar. Again, when on 

 a mission with the same object to the eastern coast of Ireland three 

 years ago, I was shown by my colleague, Mr. McHenry, certain 

 phenomena in the Silurian volcanic rocks of Portraine, attributed 

 by him to earth-movement, 1 but not much resembling the crush- 

 conglomerates with which I was then acquainted. These also I 

 now find are analogous in some respects to structures in the Manx 

 Carboniferous volcanies. 



I should like to point out that the behaviour of the lime- 

 stone in the sections which I have described affords striking 

 confirmation of the view insisted upon by Mr. Marr in a paper 

 recently brought before this Society, 2 as to the extraordinary facility 

 with which this rock is moulded and squeezed into abnormal 

 positions under earth-movement. In that paper Mr. Marr sought 

 to explain the knoll-like structures in the limestone of the Craven 

 district as having been caused by anticlinal overthrusting of a 

 peculiar type, in some respects akin to that now described in the 

 Manx volcanic rocks. In the discussion after the reading of the 

 paper I referred to the presence of small knolls of limestone on the 

 shore at Poolvash which I believed to be similar to those described 

 by Mr. Marr. These I had previously held to be original structures, 

 possibly due to the rapid consolidation of shell-banks and their 

 subsequent erosion by currents. 3 



The Poolvash knolls lie just outside the present margin of the 



1 See 'Nature,' vol. liii (1896) p. 414. 



2 ' On Limestone-knolls in the Craven District of Yorkshire & Elsewhere 

 ^uart. Journ. Geol. Soc. vol. lv (1899) pp. 327-358. 



3 Brit. Assoc. ' Handbook to Liverpool & Neighbourhood ' (1896) p. 174. 



