S. 0. Sargent — Clay-bands in the Crich InUer. 409 



of the clays. It would be easy to quote analyses of true sediments 

 bearing an equal I'esemblance to these in their main features. Tliere 

 is, however, one point worth noting. No carbon, either free or in the 

 form of hydrocarbons, was found in any of the clays under 

 discussion. 



Summary and Conclusions. 



The first and second of these clay-bands have been considered by 

 recent geological writers to be of sedimentary origin, as will be seen 

 from the following references. Of the third and fourth bands I have 

 found no mention by any writer. 



The Geological Survey memoir. North Derhyshire, 2nd ed., 1887, 

 refers as follows (p. 82) to the second clay-band in Cliff Quarry and 

 the underlying limestone : "The upper surface [of the underlying 

 limestone] is very curiously water-worn into furrows and pot-holes, 

 some of the latter being as much as two feet deep.' We have already 

 noticed that the surface of the limestone beneath a toadstone bed is 

 sometimes marked in the same way, and supposed it to have been 

 done by water, charged with carbonic acid, trickling along between 

 the beds.^ The clay-band holds about the same position in the series 

 as the toadstone at Ashover and the first toadstone at Matlock, but 

 it has not in the least the look of a decomposed lava or ash." 



It is difficult to understand the last statement, except as regards 

 the central portion of the second clay where it is black and friable as 

 above stated. Many of the clays, which are recognized as decomposed 

 toadstone, in the limestone of Derbyshire are remarkably similar in 

 the field to the clays under discussion. 



Mr. C. B. Wedd, in the Geological Survey memoir, Explanation 

 of Sheet 125, 1908, p. 18, states that "the white limestone [in the 

 inlier] includes occasional bands of shale two feet thick or more " ; 

 which can only refer to these clay^bands. Again (p. 19), he describes 

 the clay- band exposed in the Old Quarry as " a bed of ochreous marl 

 about three feet thick", and (p. 20) the first clay -band, where seen in 

 Hilt's Quarry, as " a bed of shaly marl of which the top is level ". 



I venture to think that the following features, described above, are 

 difficult to reconcile with the sedimentary view : — 



1. The abrupt transition from a clay, 2 or 3 feet in thickness, to 

 massive limestone which was evidently laid down in deep and clear 

 waters, both above and below the clay (except as regards the thin- 

 bedded limestone above the first clay). 



2. The absence of organisms (microscopic or otherwise) except in 

 one special instance mentioned above. 



3. The absence of original clastic quartz — an invariable and 

 generally abundant constituent of true sedimentary clays — the waste 

 of a land- surface. 



4. The absence of carbon, either free or in the form of hydro- 

 carbons, of which all sedimentarj' clays appear to possess a proportion, 

 frequently a very minute one. This constituent is often held in 



' 'Pot-holes,' up to 6 feet in depth, have recently been exposed below the 

 clay-band in the Old Quarry. 



- Cf. H. H. Arnold-Bemrose, op. cit., p. 204. Also "The Toadstones of 

 Derbyshire" : Q.J.G.S., vol. Ixiii, p. 253, 1907. 



