352 A Ramble in West Shropshire. 



till, as in this neighbourhood, some six or eight would be 

 formed. 



With all respect for the illustrious propounded if not the 

 author of this theory, a tourist may be excused if certain 

 questions suggest themselves to hi3 mind before he can admit 

 it, as a completely satisfactory solution of the problem ; and 

 when he considers that the opinion of geologists, as to what 

 are, and what are not really volcanic rocks, has of late years 

 been considerably modified, he may desire to know something 

 more of these " felspathic ashes/'' their composition, history, 

 and origin, before deciding the question. It is certainly very 

 striking how frequently in rocks of this age, these alternate 

 layers of shale and grit occur. At the Briedden they are con- 

 spicuous, and Sir R. Murchison describes them as occurring in 

 " The rocky tracts extending from Llandegley and Llandrindod 

 by the hills of Gelli Gilwern, and Oarneddan to Builth," at 

 Festiniog Tom-y-bwlch, and Cader Idris, etc. The occurrence, 

 however, of somewhat similar alternations in other strata, 

 though not perhaps so distinct and striking as they are here, 

 may lead some to conclude that a more general law may be 

 found to account for them, and that possibly they may only be 

 another instance of that segregative force which we have had 

 occasion to remark upon already — a force dividing the elements 

 of these primeval rocks into their constituent parts, the clay 

 separating itself into distinct beds, and the gritty and the 

 more crystallizable materials also uniting into a stratum. 

 Possibly this very tendency to crystallization may be the prime 

 mover in the whole process, just as, to use a familiar illus- 

 tration, it will cause the sugary portions of a pot of jam which 

 has been kept long enough, to segregate into a layer distinct 

 from the less crystallizable portion. 



The Llandeilo rocks are succeeded, according to the 

 opinions of the best geologists, by the Caradoc, or Bala series. 

 These are largely exhibited on the east of the Longmynd, 

 i.e. j in the Caradoc, and the country to the north and south 

 of that striking hill, but are not found on the west, where the 

 Llandeilo are immediately succeeded by much more recent 

 rocks, such as the Wenlock shale, the intervening strata being 

 omitted. 



That there is a real distinction between the Caradoc or 

 Bala beds, and the Llandeilo beneath them, there seems to be 

 reason to doubt. Professor Ramsay says, " The community of 

 the ordinary species of fossils in the Llandeilo and Caradoc or 

 Bala beds induces me to treat them as one group f 9 and Sir 

 R. Murchison himself speaks very cautiously about their sepa- 

 ration, saying, " It is not pretended that a line can anywhere 

 be precisely drawn upon a map between these strata." And, 



