EXPLANATION OF THE PLATES. 



PLATE 25. 



Fossil Shells found in the slate of Tintagel and of Snowdon. 



P L A T E 26, 



Represents a Shifted vein in the ^Lijii^st^e, with explanatory diagrams. 

 Fig. 1. Represents a fragment of -the!' miHstone whh the present appearances of 



the disjoined parts of tlie vein. * ^ ' 



Fig. 2. An attempt to replace the! vein in its otig'inal position. The dotted lines, 

 ' which represent the directions taken by the separated parts of the vein, 



also indicate the intervals of tli^laminae to the sliding of which the present 



appearances must be attributed. The want of parallelism in their relations 



is intentional, for the purpose of gaining sufficient space to represent each 



part distinctly. 

 Fig. 3. Represents a similar vein traversing a number of parallel laminae, in its 



natural position. 

 Fig. 4. The same vein after the motion of the laminae, with the effects that 



would follow both in its own appearance and in the shape of the including 



rock. 



PLATE 27. 



Chlorite crystals and vegetable remains in quartz and chalcedony. 

 Fig. I. Shews the vermicular accumulations of chlorite crystals which occur in 



quartz. 

 Fis:. 2. The same maonified. 



Fig. 3. Supposed from its structure to be a conferva : — in a chalcedony. 

 Fig. 4. Another similar substance in a similar situation. 



o 



PLATE 28. 



Fig. 1. Shews the veins of granite passing into the schist in the Mourne 

 Mountains. The upper, or lighter tinted part represents a portion of the 

 granite which forms the summit of the mountain, the lower dark part the 

 schist, into which the veins of granite run. At the mouths of the veins are 

 sometimes seen small insulated pieces of the schist. 



Fig. 2. Shews t!ie peculiar disposition of the colouring matters in the killas 

 rock at the Gun Wharf, Plymouth Dock, described in Dr. Mac Culloch's 

 paper, page 399. 



