GEOLOGY. 31 



The organic remains of this interesting deposit have as yet 

 only been found on the western side of the Den, where the 

 strata are abruptly cut off by the greenstone trap referred to ; 

 but, in following out the dip to the eastward, little doubt can be 

 entertained of their equally rich distribution in that quarter. 

 The rock there attains its greatest depth and elevation, show- 

 ing a breast of several hundred feet of variegated marls and 

 sandstone {see Yignette). It is here, at the bend occupied by the 

 mills, that the structure of the rocks and the perspective of the 

 valley are seen to the greatest advantage — the deep-tinged 

 yellow masses and mottled stripes rising overhead, enlivened 

 and beautifully diversified by running streams, leaping water- 

 falls, and tangled thickets of the bracken and milk-white thorn. 

 The hand of art, in cutting the precipitous face of rock, has 

 greatly enriched the scene, and given facilities to the geologist 

 in admitting him to the richest and finest tract of fossil re- 

 mains that ever gladdened his eyes or adorned his cabinet. 



It is a lovely place, and at the side 



Rises a mountain-rock in ragged pride, 



And in that rock are shapes of shells, and forms 



Of creatures in old worlds. ... 



But no ! the shells are not in the yellow sandstone. They are 

 nevertheless in the nearest vicinity, and in the mountain lime- 

 stone of the neighbouring coal-field they exist in countless 

 myriads. Dura Den exhibits, in the closest juxtaposition, the 

 wonders of the two geologic ages. A step carries you from 

 the one series of rocks to the other ; and, leaping across the 

 stream, in this narrow dell, you pass the shadowy bourne 

 which separates two of the oldest and most singular epochs in 

 the world's history. The epoch of fishes of the most remark- 

 able characters — the shining enamelled ganoid class — is suc- 

 ceeded by the epoch of vegetables, all nearly of tropical climes, 

 of the most exuberant growth and afiiuent abundance. The 

 mighty operations are marked here on a small scale, though 

 recorded in the most legible characters. A slight depression 



