4 TIDESWELL DALE QUARRIES. 



were held before a brisk fire, it would be produced. In 

 a section by the roadside in TideswelL Dale, above the quarry, 

 is a bed of what appears to be hardened clay, but which is 

 most probably a volcanic mud, in which the columnar structure 

 is exceedingly well shown on a small scale. The columns seldom 

 exceed an inch in diameter, and run to a considerable length, being 

 transversely divided by cracks which traverse several contiguous 

 columns. The bed is about nine feet in thickness. This was 

 seen on a somewhat larger scale in the quarry itself some time 

 ago, when the columns averaged two or three inches in diameter, 

 having a length of ten feet or more. This bed is not to be seen 

 now. The relation of the bed on the roadside to the toadstone 

 is not well seen, but in the quarry it immediately underlay 

 it. There can be no doubt that the structure was produced in 

 the mud by contact with the hot bed of lava. 



Another peculiarity of structure, well seen in the quarry, is that 

 known as " Spheroidal." Before describing it, however, it would 

 be well to again mention the relation of the various beds in 

 the quarry. We have, forming the floor of the quarry, a grey lime- 

 stone, containing the hard paits of innumerable coral animals. 

 This is overlaid by the bed of columnar volcanic material pre- 

 viously referred to, and this is followed by a rock, having a dirty 

 black appearance — the " toadstone." The face of the quarry 

 consists of this rock, and presents a peculiar appearance. It 

 appears as though, when in a plastic condition, it had sustained a 

 siege, and the cannon balls had imbedded themselves in its mass. 

 These are the "spheroids" mentioned above (Fig. 5, sectio?i). If 

 one of them be struck smartly with a hammer, one or more concentric 

 shells or coats will fall away from the globular mass, and another 

 knock may bring away several more. Indeed some of them possess 

 as many as fourteen or sixteen coats, enclosing a hard nucleus or 

 kernel — they cannot be likened to anything better than an onion. 

 In size they range from two to nine or more inches in diameter. 

 This structure has been observed elsewhere. The segments of 

 columns of volcanic lavas often contain these spheroids. The 

 drawing (Fig. 3) is a sketch of the famous Cheese Cellar or 



