Vol. 51.] ' CRUSH-CONGLOMERATES ' OE THE ISLE OF MAN. 591 



(2) ' The Crush-Conglomerates/ 



The slides from the crush-conglomerate belong to two groups — 

 those which are taken from individual fragments or ' pebbles,' 

 generally the larger ones, and those which show the microscopic 

 aspect of the conglomerate itself and its smaller 'pebbles.' 



The fragments exhibit a great uniformity in composition, and 

 nothing has hitherto been found in them but grits and slates. Now, 

 Mr. Lamplugh has shown by field-evidence that the location of the 

 brecciation has been settled, in the majority of cases, by the existence 

 of thin grit-bands in slate forming a transition between the main 

 grits below and the slates above, in the Skiddaw Series. The 

 fragments found in the crush-conglomerates could all be matched 

 either in this transition series or else in the main grits or slates. 

 Although Mr. Lamplugh was alive to the importance of looking out 

 for the existence of fragments of igneous rock and other strangers, 

 and collected a number of specimens to be tested with this point 

 in view, not a single fragment of any other rock has been up to 

 the present detected. To enforce this point five specimens of grit- 

 fragments have been selected for description, and will be dealt 

 with after the characters of the conglomerate have been described. 



(a) Two specimens and four slides of the ' crush-conglomerates ' 

 have been chosen for description : — 



[E. 2413.] — Lowest crags on eastern side of Sulby River, at 



Cluggid Junction. (PI. XX. figs. 1-4.) 

 [E. 2412.]— Druidale Stream, north of Close. (PI. XX. fig. 5.) 



A remarkable feature about these rocks is that, in spite of the 

 immense amount of mechanical disturbance which they have 

 undoubtedly undergone, they have suffered comparatively little 

 mineralogical change. The specimens previously described exhibit 

 locally much more mineral change than has been detected in the 

 zone of crush, so that the amount of change found in particular 

 specimens of the conglomerate, such as [E. 2412], need not neces- 

 sarily be connected with the actual brecciation. A specimen to be 

 subsequently described will show that the conglomerate itself has 

 sometimes suffered from a later thermal metamorphism. 



[E. 2413.] — This specimen breaks with a slabby fracture, which 

 is seen on the cut surface to correspond to a banding of the speci- 

 men, at the first glance resembling bedding. This direction corre- 

 sponds with a grit-band traversing the fine slaty material in the 

 middle of the specimen. Parallel with this, on each side, run one 

 or more bands of conglomerate, generally consisting of light-coloured 

 fragments in a darker matrix ; some of the fragments are, however, 

 darker than the matrix. Traversing all these bands at an angle of 

 about 30° or 35°, runs a close cleavage, the planes being lead- 

 coloured and marked by a deposit of exceedingly fine chloritic 

 matter. This is the ' shear-cleavage ' of Mr. Lamplugh, and its 

 intersection with the slabby structure produces a streaking on the 



