Vol. 51.] CRUSH-CONGLOMERATES OE THE ISXE OF MAN. 567 



It is affected by an imperfect cleavage ('shear-cleavage') 1 

 later than the brecciation. Several igneous dykes which intersect 

 it are affected by the same cleavage, though not by the earlier 

 crushing. 



From the mouth of Sulby Glen the crush-conglomerate extends 

 eastward for 4 miles farther, to Ramsey, at first in outcrops having 

 a horizontal breadth of over a mile, but afterwards in a series of 

 comparatively narrow subparallel bands ; and it is suggested that 

 these exposures represent the emergence of a deformed plane. 

 At Ramsey its farther course is cut off by the intervention of a 

 bank of drift, just before it reaches the east coast. In many localities 

 the sections show clearly every stage in the formation of the 

 crush-conglomerate. 



(2) Detailed Account of the Sections. 



The more closely the Skiddaw Slates of the Island are examined, 

 the more evident does it become that they have everywhere suffered 

 deformation and shear. Strata in which the bedding-planes appear 

 ■at a first glance to be quite regular will be found on nearer examina- 

 tion to have their thinner layers pinched or puckered out so 

 frequentty, that any particular lamina can rarely be traced for more 

 than a few feet or yards. Sometimes, where the beds have been 

 stretched, the laminae disappear against each other obliquely as in 

 faint cross-bedding ; and again, where packing has taken place, 

 the lines of stratification are confused in a series of wrinkles, which 

 emerge on the bedding-planes as small parallel folds closely resem- 

 bling ripple-marks (see figs. 3 & 4, pp. 570, 571). In the finer- 

 grained flaggy beds the surfaces are sometimes tesselated by narrow 

 regular pleats in parallel sets crossing each other obliquely, some- 

 what resembling ' sun-cracks ' in aspect ; and in the more homo- 

 geneous argillaceous deposits the whole mass is frequently striated 

 throughout with shear-cleavage, sometimes in two different direc- 

 tions, to the more or less complete obliteration of the original 

 bedding. In general terms, these structures may be summed up 

 as indicating acute folding, accompanied or followed by a shearing 

 fluxion-movement usually along the planes of bedding, with the 

 later development of obscure cleavages obliquely across the folds. 



Many of the igneous intrusions also, especially the narrower dykes, 

 have been so greatly sheared that their crystalline constituents have 

 been disintegrated. Sometimes, indeed, the dyke has become quite 

 schistose, and its margin frayed out into the enclosing slates. 



These indications are, on the whole, most acute on the north- 



1 Throughout this paper I have, perhaps somewhat arbitrarily, used the 

 term ' shear-cleavage ' to denote the imperfect cleavage (to some extent a 'strain- 

 slip cleavage ') which usually affects the rock as a mass and determines its 

 fracture ; and have confined the term ' strain-slip ' to the wider-placed and 

 better-defined planes of slipping or ' close-joints-faulting ' which are more 

 intimately connected with the brecciation-movements. As will presently be 

 shown, the 'shear-cleavage' is of later date than the brecciation, while the 

 ' strain-slip ' planes are at least as old as that movement. 



2 s 2 



