FURTHER NOTES ON TIDESWELL DALE QUARRIES. 



fact, the tendency is to a radiate structure by means of more 



or less distinct cracks 

 arranged in that manner, 

 and more pronounced to- 

 wards the centres of the 

 nodults. Another wide dif- 

 ference is in the jointing 

 of the two rocks, and the 

 relation of the spheroids 

 to them. At Tideswell, 

 the jointing is precisely as 

 in those parts of the same 

 rock where spheroids are 

 absent — an irregular ar- 

 rangement of cracks 

 (CCCC), without any ap- 



Fig- 5- 



parent order, breaking up the rock into irregular polyhedral 

 masses, each being the seat of a spheroid (when present), the 

 subordinate (or spheroidal) system of jointing of which, gives 

 rise to the nucleus and its succession of concentric shells. 

 But at Cader only one system obtains — the rock-joints ; 

 and it is their peculiar curvy arrangement that break the 

 rock up into these nodular masses — just as it is the peculiar 

 geometrical arrangement of the rock-joints which give rise 

 to prismatic structure in basalt. Hence, while it is right 

 to speak of these latter as Nodular (I prefer this name to 

 "Spheroidal," in this case) and Prismatic structures, I deem it 

 more correct, in the former case, to speak of the rock as 

 Sfiheroidiferous. 



We will not enter into the difficult subject of rock-joints — 

 sufficient it is for us that the jointing of the two varieties of Toad- 

 stone, above mentioned, is identical. How came the Spheroids ? 



i. The Toadstone above mentioned : as yet I have found 

 only one variety of this rock to be spheroidiferous ; and, 

 in this, as already intimated, the presence of spheroids 

 is by no means the rule. This variety is a dense, 



