Vol. 55.] THE ASHBOUENE AT^D BUXTON EAILWAT. 227 



Ifc has, in fact, been subjected to the same foldings as the beds 

 above and below it. 



The ash is generally of a rather coarse texture, has in many places 

 a distinct lamination, and contains numerous blocks of a dai^kblue or 

 grey amygdaloidal rock, distributed irregularly throughout its mass. 

 A thick bed of volcanic ash also occurs at the southern end of the 

 cutting. It is much decomposed, and only the upper 36 feet of it 

 is seen. It is overlain by a succession of shales and thin lime- 

 stones (some of which, are tufaceous) with thin partings of tuff. 

 The limestones often contain chert, Productus, and encrinite-stems, 

 and in places are dolomitized. The beds at first dip in a north- 

 easterly direction and then become bent into a number of troughs 

 and arches. The railway turns northward, the beds dip south-west- 

 ward, and under the shales one again finds the bedded ash. 



The occurrence of four exposures of ash in this and in the next 

 two cuttings led me to try and ascertain whether they all belonged 

 to the same deposit, or were due to several eruptions. They all 

 occur within a mile of Tissington, and one would hardly expect to 

 find, within so short a distance in this district, evidence of several 

 great outbursts, each followed by a succession of more feeble 

 eruptions. 



The structure of the ground, the numerous folds into which the beds 

 have been thrown, and the fact that the country is largely covered by 

 Drift, render it difficult, if not impossible, to connect directly the four 

 outcrops of ash by tracing their relations in the field. I have already 

 mapped a large area of ground covered by the second exposure of 

 ash, through which the central portion of Tissington cutting passes, 

 in order to trace it, if possible, to its source. But it would be beyond 

 the scope of the present paper to enter into any further details 

 regarding the surrounding country, and that part of the subject 

 must bo left until I have more fully worked out the rocks of the 

 district. I have been able, however, to trace this ash in a northerly 

 direction, up to within a short distance of the third exposure of ash, 

 which is seen in the Highway Close Barn cutting (p. 229). 



In order to ascertain whether the two beds of ash in the Tissing- 

 ton cutting belonged to the same deposit, I made careful measure- 

 ments of the thickness of the beds, at right angles to the bedding- 

 planes, from one end of the cutting to the other. I measured from 

 the southern ash up to the top of the first syncline, then down to 

 the base of the adjacent anticline, and so on, to the second exposure 

 of ash : the total up-and-down measurement differed by 6 feet. I 

 then plotted ten vertical sections to scale, and found that the ash at 

 the second exposure was 6 feet lower in the series than that at the 

 first. The measurements were then checked in several ways in 

 the field, and the difference of 6 feet was found to hold good. 



A comparison of the sections showed that there were several well- 

 defined beds of limestone, one of which appeared six times, and 

 another three times in this part of the cutting above the ash. The 

 lower of these two beds is denoted by the letter A, and the upper bed 

 by the letter B, in PI. XVII, fig. 1, and in PI. XVIII, figs. 1 & 2. 



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