Vol. 51.] ' CRUSH-CONGLOMERATES ' OF THE ISLE OF MAN. 595 



"been affected by crushing, as is shown by the character of a slide 

 taken from beneath the crust of the block. Microscopically this 

 slide is seen to consist chiefly of quartz-grains, the largest of which 

 are a little over '02 inch in diameter. Some of these are rounded 

 and marked off from the matrix by a deposit of dark material. The 

 smaller grains, which are angular, vary from "01 to *005 inch in 

 diameter. One of the grains contains a felsitic inclusion, as though 

 the quartz had been derived from a quartz-porphyry, and a few 

 of the grains answer to the matrix of such a rock. Very few 

 grains of felspar, and one or two of detrital tourmaline, are present. 

 The matrix is quartzose, with a little sericite and much chlorite. 

 The rock shows no signs of crushing or shearing, and there is 

 practically no new mineral development in it. 



The finer grits [E. 2410 and 2421] have suffered much more 

 from crushing. The first contains abundant grains of felspar, as 

 well as of quartz and muscovite, together with particles of iron ore. 

 Many of the quartz-grains are composite, and have been derived 

 from a granitic or gneissose rock. The grains of felspar are fre- 

 quently dusty with inclusions and decomposition-products interiorly, 

 but are surrounded by a ring of water-clear felspar in optical 

 continuity with the interior. 



The grains average *006 inch in longest diameter; the fine matrix 

 is made up of quartz, twinned felspar, and muscovite. The smaller 

 grains are arranged with their long axes parallel to the plane of 

 movement, and the matrix is chiefly occupied by folia of sericite 

 which wrap round the grains and are evidently a secondary product 

 due to the movement that the rock has undergone. The patches of 

 iron ores are broken to dust, and spaced out in lines parallel to the 

 movement. 



[E. 2421] is somewhat similar, but it is not so much crushed or 

 altered. 



The next specimens [E. 2411 and E. 2419] are of great interest 

 because, while collected as single fragments in the conglomerate, it 

 is quite evident that a little further crushing would have converted 

 each of them into many fragments with ' matrix ' material between 

 them, and would have incorporated them in the body of the eon- 

 glomerate. 



[E. 2411.] — A coarse, dark, quartzose grit, in which some of the 

 quartz-grains are opalescent. The original sedimentary arrange- 

 ment of the materials of this rock is entirely lost, and the structures 

 which are left are merely those due to movement. The rock has 

 evidently been a coarse quartz-felspar grit in which quartz predo- 

 minated, but fragments of slaty and felsitic rocks were also present. 

 The quartz-grains are phacoidal in outline ; they often possess 

 undulose extinction, and they have at times an appearance of 

 twinning. They are often made up of one, two, three, or even 

 more inosculating portions, and they can be seen beginning to 

 divide, the separated portions becoming filled with granular quartz, 

 and every transition down to complete granulation can be followed 

 up step by step (see PI. XXI. figs. 4 & 5). 



Even when a grain as a whole has withstood the crushing force, 



