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N."W. direction, i.e., in the same tlirection as the principal axis of the "Woolhope 

 Valley; and the cross faults which transverse this are N.E. by E. nearly the 

 same lines as those of Mordiford, Putley, &o., in the 'Woolhope disti'ict, There 

 are also E. and W. faults in both of small amount, and some North. 



The chief difference then is due to the great change in mineral character, 

 Throughout the greater part of Sovith "Wales the "Wenlock rocks are of a sandy 

 nature, becoming indeed quite hard sand rock in places. The Silurian districts, 

 Woolhope, Malvern, Dudley, &c., during the same period were covered by deeper 

 and more tranquil water, depositing limestone and shale in succession. Now 

 the change from one ef these to the other commenced in the Usk district, and 

 hence it is that while in the valley of "Woolhope there is soft shale full of 

 ordinary "Wenlock fossils, at Cilfigan park and Glascoed common, Usk, it was all 

 strong sandstone (with such shells as loved shallow water and a sandy bottom) 

 in "Wenlock times. The lower Ludlow indeed is somewhat more of the ordinary 

 kind, but only in the northern parts of the district. At Glascoed common and 

 further south it is a sandy rock also, unless there be strange faults not yet dis- 

 covered. The limestones are thin, as we might expect, in deposits nearer shore. 

 There is a further difference in the top of the Ludlow rock. The Downton 

 sandstone is represented by a thin grit and shale at "Woolhope, but it is a thick 

 series of grey and purple grits round Usk, a rock so hard as to form higher 

 grouhd than the neighbouring Ludlow beds. Its thickness is not yet known ; 

 but must be considerable near Llandewifach and Llandegfydd, where Mr. J. E. 

 Lee first discovered it. It is met with along the northern edge at Clytha 

 House. Its thickness there is not known, nor is it to be seen in its place at the 

 Chain bridge, though there is clear evidence of its having covered the upper 

 Ludlow rock there, at a place where the Ludlow rock has no business to be 

 except for a great fault. To this fault I wish to direct attention presently. 

 But it is to be observed that the hard gritty rock which represents the Downton 

 sandstone, though here and there showing traces of land plants, was deposited 

 on a more open shore than the true Downton sandstone of Ludlow, Malvern, and 

 "Woolhope; The great number of Lycopodiaceous seeds, named Pachytheca by 

 Hooker, or Pachygporangium (for both names are extant), must have been drifted 

 down by rivers, for there is no appearance whatever of this plant, whose form 

 indeed is unknown, having grown in the sea-water, as the plants of the coal 

 did. The typical Downton sandstone, then, is an estuary bed, and the fine 

 sediment supports this idea. But the red and purple grey rock of the Usk hiUs 

 is not only much thicker than the Downton sandstone, but is decidedly coarse 

 and conglomeratic, frequently a grit, always a roughish sandstone, and not 

 unfrequently coarse conglomerate. The spines of shark-like fish occur in it on 

 the west side of the district, trilobites and shells on the south border. It is 

 traceable even as far as Cardiff, but of that we need not speak here, except to 

 show the prevalence of faults of great extent all over South "Wales, It is more 

 to the point to notice that this red grit, which contains only Ludlow rock species, 

 fish and shells, is to be traced from this point all along the edge of the Silurian 



