22 MR. G. W. LAMPLTJGH ON SOME EFFECTS OF [Feb. IC,OO y 



Volcanic Series and must once have been overlain by the tuff. 

 They occur in a limestone which, I think, must have originally 

 possessed a lenticular structure, but I should now admit that, 

 whatever its original arrangement, the limestone at this point was 

 implicated in the movements which have affected the volcanic rocks. 

 It may be added, however, that on examining the Craven knolls 

 during the past summer, I found less similarity between them and 

 those of Poolvash than I had anticipated, and that I should now 

 hesitate to regard the structures as identical. 



VIII. Age of the Movement. 



Much light as to the age of the movement has been obtained from 

 the deep borings recently made in search of coal on the Drift-covered 

 plain at the northern extremity of the island. These borings, 

 collectively, after passing through Drift of exceptional thickness, 

 penetrated a varied series of New Red rocks, consisting of Saliferous 

 Marl, St. Bees 1 Sandstone, Lower Marl, and Brockram, directly 

 comparable with deposits of the same age on the opposite Lancashire 

 and Cumberland coast. These Red Rocks constitute a conformable 

 and undisturbed sequence with a low regular dip, and rest on the 

 uptilted edges of Lower Carboniferous strata having a high dip and 

 showing signs of great compression and disturbance. It is usual to 

 assign an Upper Permian age to the lower part of this E"ew Red 

 Series in Cumberland ; and if this be correct, the Lower Carboniferous 

 rocks of the island must have been affected by severe movement at 

 an earlier date than Upper Permian ; irr any case it is clear that 

 the disturbances were pre-Triassic. The Peel Sandstones and Con- 

 glomerates of the western coast of the island seem to have participated 

 in these movemeuts ; and these rocks have usually, and I think 

 rightly, been considered not newer than Lower Carboniferous, though 

 a Permian age has recently been claimed for them. 1 



The movements which I have discussed may therefore be assigned 

 to some period in the interval between Lower Carbo- 

 niferous and Upper Permian times. They probably belong 

 to a single epoch, and brought about a northward overthrust of the 

 higher beds upon the lower in the south of the island. This 

 direction is towards the central massif into which the Manx Slates 

 had been compressed during an earlier cycle of earth-movement. 



Discussion. 



The President, after congratulating the Author on his paper, 

 read the following extract from a letter that he had received from 

 Sir Archibald Geikie, who was unable to be present : — 



' Having been twice with Mr. Lamplugh over the ground which 

 lie describes, the second time quite recently, since his present views 

 as to earth-movement were formed and matured, I am glad to bear 

 my testimony to the exhaustive care which he has expended on the 



1 W. Boyd Dawkins, Trans. Manch. Geol. See. vol. xxii (1894) p 590 & 

 Toi. xxiii (1895) p. 147. 



