303 



Crush-couglomerates of the Isle of Man." (6) The rocks showing 

 the special features of crush belong to the Skiddaw Slates 

 Series, composed of alternating grits and flags with fine 

 argillaceous shaly slates. The width of outcrop of the crush- 

 conglomerate, in one place, measures 400 yards across the 

 strike, with a vertical depth of over 500 feet. Other sections 

 of a like kind occur over the area of 200 square miles occupied 

 by the rocks of this age on the island. The brecciation has 

 taken place in the passage beds between' the gritty beds and 

 the fine slaty series. It is not-eworthy that, in places where 

 the rock is fresh, the broken fragments can scarcely be dis- 

 tinguished from the base, but on weathering a difference of 

 colour is developed between the inclusions and the matrix. 



The great thrust plane that occurs in North-western 

 Scotland, at the junction of the Lewisian Gneiss and Torridon 

 Sandstone has, in places, developed crush-conglomerates. The 

 Director-General of the Geological Survey, in describing the 

 work of Messrs. Peach and Home in elucidating this classic 

 geological region, saySjC^^ ''For nearly a mile to the east of 

 its junction with the Torridon Sandstone the Lewisian Gneiss 

 has undergone so much mechanical deformation as to pass into 

 fine flaser-gneiss with a platy structure. In some caaes, 

 indeed, the alteration has been so great that all the original 

 structures of the gneiss have entirely disappeared, and it is 

 then hardly possible to determine from what original types 

 the rocks, as we now see them, have been derived. 

 Immediately east of this flaser-gneiss, beyond Kirkton of Loch 

 Alsh, an important band of moine schist, about 300 yards 

 broad, has been thrust over the gneiss, and is again succeeded, 

 on the east side, by massive acid and basic gneisses of 

 recognizable Lewisian types. These latter rocks present on 

 the headland to the south-east of Kirkton of Loch Alsh some 

 remarkable examples of pseudo-conglomerate structure, bands 

 of chloritic and actinolitic schist enclosing rounded and oval 

 masses of biotite- gneiss and small rounded blocks of quartz. 

 The deceptive resemblances to conglomerate have doubtless 

 been produced by mechanical movements. The several bands 

 of gneiss having first been plicated and then subjected to 

 still further crushing, whereby lenticular pieces of these were 

 wrenched off and arranged with their long axes parallel with 

 the foliation planes of the schist. These separated pieces are 



(6) Quar. Jour. Geolog. Soc, vol. li. (1895), pp. 563-588, 

 with a Petrographioal Appendix by Prof. W. W. Watts, pp. 

 588-599. 



(V) Ann. Reports Geolog. Survey of United King, for the vear 

 1895, in "Forty-third Report of Dept. of Science and Art," Vol. 

 XXX., 1896, Appendix E, p. 294. 



