408 //. C. Sargent — Claij-hamh in the Crich Inlier. 



The clays consist of stiff, plastic material, containing much moisture 

 when first exposed, generally of a bluish-grey colour, and freql^ently 

 with ochreous upper and lower surfaces, the variations in colour 

 being apparently due to varying (juantity of iron oxides. The central 

 portion of the second clay, where exposed in Cliff Quarry,' is black 

 and friable, but it does not show these features elsewhere. Minute 

 cubes of pyrites are sporadically abundant throughout the clays. 



With the exception of the first, which is generally covered by 

 thin-bedded rock, all the clay-bands are intercalated between massive 

 beds of limestone, without any gradation from limestone to clay, 

 above or below. 



After careful examination I have been unable to find any traces 

 of organic life in these claj-s, with the exception of the black central 

 portion of the second clay-band where exposed in Cliff Quarry. 



The surface of the rock below the clay-bands is always found to be 

 hummocky or mammillated, and not infrequently worn into deep 

 farrows and holes, much resembling 'pot-holes', which are always 

 filled with the clay. 



Very similar clays, or ' way-boards ' as they are called by miners, 

 a term adopted by geological writers as far back as Whitchurst 

 (1778), are frequently seen in other parts of the limestone of 

 Derbyshire, and have been long recognized by their field relations to 

 be decomposed toadstone. Thus, Farey (1811) says: "In many 

 places it [toadstone] appears, both in deep Mines and at its basset, as 

 a plastic Clay, often of a bluish grey colour, where the numerous 

 Meers or Cattle-Ponds of this district occur upon its basset 

 edge, . . ."2 



Microscopic Structure. 



A process of careful levigation and mici'oscopic examination of their 

 heavier constituents, after removal of the finer nuid or ' clay- 

 substance', show that these clays contain little or no quartz, but 

 a fair amount of decomposing felspar, chloritic material, and sometimes 

 abundant pyrites in minute cubes. Thin sections of material from all 

 the exposures named above appear to bear out the same result. wing- 

 to the mass of opaque matter it is not always easy to identify the 

 minerals, but chloritic and felspathic material are seen, with perhaps 

 a little secondary quartz. One of the sections, that of a specimen of 

 the second clay-band from Hilt's Quarry, is especially interesting, in 

 that it shows radiating aggregates giving a black cross in polarized 

 light of a secondary mineral formed in the clay, which I have not 

 been able to identify. It may perhaps be epidote. 



Chemical Composition. 

 Below are given analyses of the clays and also, for purposes of 

 comparison, of typical Derbyshire lavas decomposed to clay. The 

 resemblance is striking, but by no means conclusive as to the origin 



' Cf. H. H. Arnold-Bemrose, " A Sketch of the Geology of the Lower 

 Carboniferous Eocks of Derbyshire": Proe. Geol. Assoc, vol. xvi, p. 177, 

 1899. 



" General Vieiv of the Agriculture and Minerals of Derbyshire, vol. i, 

 p. 278. 



