Vol. 51.] ' CRUSH-CONGLOMEEATES ' OF THE ISLE OE MAN. 589 



tion, shearing, and cleavage, the influence of those movements 

 which have produced such grand results in the great crush-zone 

 itself. These rocks may be regarded as the raw material out of 

 which the ' crush-conglomerates ' have been manufactured. 



I do not propose to give a full microscopic description of each 

 specimen, only of those which are of prime importance, merely 

 referring to the principal features which are to be observed in the 

 other specimens. The sediments are best illustrated by the follow- 

 ing examples : — 



[E. 2403. 1 ] Glen Dhoo Stream, nearly 2 miles west of Sulby 



Glen. A crushed grit. 

 [E. 2414.] Eastern side of Glen Dhoo Stream. Grit cut into 



'pebbles' which are only just being disconnected. 



(PI. XXI. figs. 1-3.) 

 [E. 2427.] Same locality. Close-grained grit. 

 [E. 2415.] Eoadside, S.E. of Snaefell. Striped and puckered 



slate. 

 [E. 2416.] Traie ny Foillan, Maughold. Striped sandy shale, 



frilled and sheared. 



[E. 2403.] — A dark-grey, compact grit, with veins running 

 parallel to the shear-planes. Microscopically this grit is seen to be 

 made up chiefly of quartz-grains with a smaller quantity of felspar 

 and a few bits of detrital mica and tourmaline. The largest grains 

 measure *02 inch in length, but the average size varies from -005 

 to '007 inch in length. In part of the slide the grains show the 

 effects of crushing, and have become phacoidal in shape ; the shear- 

 planes which curve round them are marked by sericite-flakes. The 

 matrix, in which the grains are set, is a very fine-grained aggregate 

 of quartz-grains, calcite, and minute scales of sericite ; the latter 

 mineral, from its relation to the fragments, occasionally encroaching 

 on even the larger grains, must be a secondary product. 



[E. 2427] is a still finer grit, which is more crushed than that 

 last described, so that all the grains are phacoidal in shape and are 

 set in a plexus of minute flakes of sericite and pale-brown mica. 

 It has evidently undergone some chemical change. 



[E. 2414.] — The two slides cut from this specimen are extremely 

 instructive, as they show fine puckered slate in contact with fine- 

 grained grit, just the kind of junction which one would expect 

 from Mr. Lamplugh's observations to throw light on the progress 

 of the crushing. The junction is irregular — rounded promontories 

 of the grit projecting into the slate, and fine crushed shreds of slate 

 running into the gulfs and bays between. 2 Occasionally bits of 

 grit are quite isolated from the main mass, and form, as it were, 



1 The numbers in square brackets are those of the slides in the collection of 

 the Geological Survey. 



2 The figures and description given by Prof. Bonney (Quart. Journ. G-eol. Soc. 

 ■vol. xl. 1884, pp. 19 & 20, fig. 9 & pi. i.) deal with a phenomenon which is 

 precisely similar to this. 



