112 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 1, 



largely exposed in the upper part of the quarries of green slate at 

 Patterdale, and in the Langdale quarries and many other places 

 in Westmoreland and Cumberland. In all these slaty breccias, the 

 included masses are flatter between the planes of cleavage than in 

 any other direction. Their irregular forms prove them to have been 

 imbedded pebbles or fragments, and cannot be explained by reference 

 to crystallization : indeed they have rarely any cr^^stalline character, 

 but consist of slate, differing more or less in grain, colour and hard- 

 ness from the matrix in which they are imbedded. In the localities 

 mentioned, the bedding is most distinctly marked, and we can judge 

 with certainty of the position of the fragments with reference to it : 

 if they had been originally flat pieces of slate accidentally deposited, 

 we should find them lying on their flat sides in the bed, but this is 

 not the case ; their flattest sides are always parallel to the cleavage- 

 planes, and consequently where the cleavage cuts the bedding at a 

 high angle, as is the case in all the Langdale quarries, and in some 

 of those at Patterdale, these thin masses appear to be standing up- 

 right in the bed on their edges ; a position which they never could 

 have reached if their forms had been originally those we now find. 

 We can only explain the circumstances by supposing that these 

 masses were flattened when the rock was subjected to a pressure 

 which acted in a direction perpendicular to the planes of cleavage. 



When we examine the outline of these imbedded masses, as it is 

 seen on the face of a sheet of slate, we usually find them to be rather 

 longer down the dip of the cleavage than across it or along its strike : 

 this confirms the opinion that the rocks have expanded in the direc- 

 tion of the dip of the cleavage. 



As we do not know the original forms of the imbedded fragments, 

 we can only guess at the amount of compression they have under- 

 gone ; but we may be certain that it has been very considerable, for 

 in many localities their thickness between the cleavage-planes is 

 seldom equal to half their diameter as seen on the planes of cleavage. 



To illustrate the forms of the fragments imbedded in the brecciated 

 slates, I have added two sketches of a piece of slate from the Patter- 

 dale quarry. 



Fig. 1 is taken from the surface of the plane of cleavage showing 

 the largest and flattest side of all the fragments, which are longest in 

 the direction of the dip of the cleavage y y/ Fig. 2 shows the side 

 of the same sheet of slate with all the fragments flattened between 

 the planes of cleavage. The hues a a represent the planes of bed- 

 ding, with a considerable dip. 



Between the well-marked slates and the great bands of porphyritic 

 rocks which traverse the "green slate" district of the Lakes, there 

 are extensive masses of metamorphic rocks more or less crystalline, 

 which appear to have been sedimentary deposits altered by the neigh- 

 bouring igneous action. In these rocks the cleavage is usually well- 

 marked, and the bedding can frequently be distinctly traced. But 

 the nearer we approach the axis of igneous action, the more obscure 

 do we find the bedding, till it is gradually lost ; the cleavage then 

 becomes more faint, and we soon reach a mass of crystalline rock 



