1870.] MELLO—TIDESWELL-DALE CLAY-BED. 703 
Turning next to the south of the quarry, once again the red 
prisms are seen at an angle of 38°. This strange-looking rock 
passes downwards into a coarse greenish-looking bed, composed of 
fragments of limestone and partings of greenish-yellow clay (c); and 
this forms a “ wadding” to a series of very excellent ornamental 
marbles, which form three principal beds with their partings ; these 
marbles are full of corals, the ramifications of which give them their 
beautiful variegated appearance. 
. Toadstone with concretionary balls ............ | 
xn very hard, dark green, and compact ; about 12 ft. 
P. 5 amygdaloidal and vesicular......... if 
6. Prismatic (clay ?), 9 ft. 
¢. Clay and Limestone, ‘“‘ wadding.” 
d. Marble with Corals, facing south. 
With regard to the red clay just described, the question which 
suggested itself to me was, whether it was a greater local develop- 
ment of that before mentioned as occurring in thin partings in the 
limestone near Litton tunnel. I am not aware of any other locality 
in the county where the clay is found altered as this is, and par- 
taking of the columnar character, which must have been caused, I 
presume, by the heating effects of the overflow of the toadstone, and 
subsequent contraction under pressure. I have seen brick-clay that 
has, on a small scale, become beautifully prismatic after heating ; 
and we have instances of clays and other rocks being altered and 
rendered more or less perfectly columnar through proximity to erup- 
tive rocks. I cannot do better, in conclusion, than quote a re- 
mark made by Mr. D. Forbes a short time since in reference to the 
igneous rocks of Staffordshire. He said that “ the sedimentary rocks 
in contact with these were themselves frequently so altered as to 
present in themselves a columnar structure or jointing, in some 
