410 //. C. Sargent — Clay-hanch in the Crick Inlier. 



solution, and is derived, as may be supposed, from the organic life of 

 the waters whicli bore such clays to tlieir resting-place. 



5. The frequent local presence of minute cubes of pyrites. This 

 mineral appears to be always of secondary origin in sedimentary 

 clays, and is supposed to be due to the reducing action of decaying 

 organic matter, sometimes through the agency of enzymes, on 

 solutions of ferrous sulphate in the sea,' Here we have no organic 

 matter to set up the reaction. 



On the other luind, the great similarity in appearance of these 

 clays, in tlie field, to clays resulting from the decomposition of 

 toadstone, is suggestive of volcanic origin. The features named 

 above, as lending no support to the sedimentary view, may perhaps 

 be held to favour this suggestion. 



The field relations with regard to the country rock, the absence of 

 original clastic quartz and carbonaceous material, and the presence of 

 pj'rites are features which these beds share with other clays in the 

 county which are recognized as decomposed loadstones. 



It must be admitted that the microscopic structure does not give 

 much positive evidence in favour of the volcanic view, but I luive 

 found nothing on any of the slides prepared from these clays to 

 negative that view. In these thin beds, satui'ated with percolating 

 carbonated waters, decomposition would probably proceed so far 

 that most of the original minerals in the basalt or tuff from which 

 they might be derived would be destroj-ed. It appears probable, 

 however, that in the initial stages of the process, the ferro-magnesian 

 constituent would be converted into the chloritic material seen on the 

 slides, and silica would be liberated by the decomposition of the 

 felspars, so that the presence of secondary quartz can be easily 

 explained. 



Further suggestive evidence may be mentioned. 



The 'pot-holes' referred to above are, so far as I am aware, only 

 found elsewhere below a toadstone bed, and there seems no reason 

 why there should be an exception to this rule in the Crich area. 



A bed of lava is known to exist in the limestone of Crich Hill 

 " at depths varying from 180 to 480 feet", - and this again indicates 

 that the area was well within the range of Carboniferous volcanic 

 activity. 



There remains a difficulty to be faced, viz. the presence of fossils 

 in a part of one of the exposures already alluded to. Dr. Arnold- 

 Bemrose describes the second clay-band, where exposed in Cliff Quarry, 

 as " a bed of black shale containing a few fossils ".^ It has been 

 mentioned above that the central portion of this bed is here black 

 and friable, in which respect it differs from the other clays, and it 

 undoubtedly contains a few fragmentary traces of fossils which are 

 always, so far as my observation goes, so badly preserved as to be 



1 Cf. H. A. Miers, Mineralogy, 1902, p. 328; also G. A. J. Cole, Ttocks 

 and their Origins, 1912, j)p. 84, 85. 



^ H. H. Arnold-Bemrose, "The Toadstones of Derbvshire " : Q.J.G.S., 

 vol. Ixiii, p. 266, 1907. 



^ " A Sketch of the Geology of the Lower Carboniferous Eocks of 

 Derbyshire " : Proc. Geol. Assoc, vol. xvi, p. 177, 1899. 



