VTT 



Tlie first-named fault along tlie Usk is no less a key to others. It happen* 

 fee bo well seen exactly opposite the chain bridge. For there, while the general 

 lie and trend of the rocks is such as that all the strata about Kemey's Com- 

 mander should be "Wenlock slial« and sandstone — dipping east under the lime- 

 stone which comes up from Trostrey — we suddenly find ourselves in ITppcr 

 Ludlow rock, dipping N.N.W., the corresponding rock to which lies miles to 

 the north, at Trostrey Lodge and Clytha Castle. 



This place is a capital example of the visible and invisible elements of 

 fault lines — for nine -tenths of the faidt here so plain lies concealed in the 

 alluvial valley of Usk. It could never be traced, but for this little section, not 

 half a mile long, and so narrow a strip, that when you mount the hiU you find 

 yourself immediately on "Weulouk sandstone in its proper place. But, using 

 experience, we might infer the fault from the outline of the country. It is not 

 easy to see otherwise why Usk Castle should be on Upper Ludlow rock, and 

 Llanbaddock Church across the river stand on Aymestry limestone, — why the 

 river should have chosen to break through limestone and sandstone, in an 

 approximately straight line, when it might have turned east or west if it were 

 only seeking an easy jiassage. And for a like and strict!;/ parallel reason, why 

 the brook which drains Glascoed Common should choose, after running south 

 for a mile or two, suddenly to turn S.E. by S. and run in a straight course, 

 regardless of the direction or hardness of the beds, for a distance of three miles, 

 exactly parallel to the Usk fault. But if I believe in faults, and look nortliward 

 to- the great gash which has severed the rival mountains above Pontypool, I 

 have no diflSculty in continuing that line by Llanfihangel and Panteg, and the 

 hills about Llandegfydd ; and in understanding by parallel and similar faults wliy 

 the Silurians are thrown uj), and the Comstones are cut asunder, before the 

 Afon Llwyd flows into the Usk. 



In conclusion, I have the honour of Siluria at heart ; and I hope that 

 the "Woolhope Club will not forget that, while the charming Woolhoiie anticlinal 

 is the prettiest and grandest exposition of the Upper Silurian Kocks in the 

 eastern region, the Usk district is that which will enable them to connect the 

 Shropshire deep-water type with the shallow- water rocks of South "Wales ; tliat 

 the study of the faults will greatly help them in tracing the beds they are 

 endeavouring to make out ; that the jjarish maps are the best for putting down 

 observations on ; and that the ti-ue way to make the club usefvd in forwaiding 

 our geological knowledge, is to take nothing in the Government Survey for 

 granted, but to use these maps as a mere outline, to be filled up and corrected; 

 by the field clubs. 



