82 Reviews — MurckisorCs " Sihcria" 



in the recognition of the geological identity of the several parts of 

 this important group. 



In the next set of deposits (the Llandovery), sandstones succeed 

 schistose and slaty Caradoc beds in South Wales ; and are there 

 divisible into Lower and Upper (at Noeth Griig) ; and the Upper 

 Llandovery is again found in Radnorshire and the border counties, 

 without the Lower member. Often full of the casts and moulds of 

 fossils, as is the case also with the Caradoc Sandstone, the Llan- 

 dovery beds have been mistaken for it, — especially the Upper 

 Llandovery Sandstone of May Hill ; but the fossils are mostly 

 distinct in species, and Pentameri abound so much that they form a 

 coarse calcareous band (Hollies Limestone) on the western side of 

 the AVorcestershire Beacon. The Llandovery beds are *' Middle 

 Silurian," but not distinctly separate from the Caradoc below and the 

 Wenlock formation above, — their fossils being not very often " pe- 

 culiar," some being found above, some below, and some both in upper 

 and lower formations ; but those of the upper part of the group 

 more especially have alliances in the Upper Silurian formations 

 which next come to be described. The "Tarannon Shales" are 

 also mentioned as either occupying, in North Wales, the place of the 

 Upper Llandovery Sandstone, or forming part of the next series 

 (Wenlock formation), the local member of which, or the " Denbigh- 

 shire Grits," there lies conformably upon them, passing upwards 

 into ordinary Wenlock Shale. This last, with its two interbedded 

 limestones, — the lower and thinner band being known as the "Wool- 

 hope Limestone," whilst the upper calcareous la3''ers have the name 

 of Wenlock or Dudley Limestone, — is the subject of an interesting 

 chapter, which illustrates also the structure of the Wren's Nest and 

 the curious Woolhope Valley of Elevation ; just as in the course of 

 the earlier chapters the physical features of Snowdon, the Breidden 

 Hills, Caer Caradoc, the Malverns, the Stiper Stones, and the Long- 

 mynd are elucidated in connection with their geological structure. 



The Ludlow formation, including the Aymestry Limestone as its 

 middle member, comes next. The information obtained of late 

 years respecting its uppermost portion, whereby it passes upwards 

 into the Devonian Sandstones of Herefordshire, is reduced to order 

 in chap. vii. ; and the interesting discovery of the remains of a fish 

 {Pteranpts Ludensis) in the Lower Ludlow beds at Leintwardine — 

 the oldest vertebrate known — is alluded to. 



The Silurian rocks of other parts of Britain, beyond the typical 

 region of " Siluria," namely, in Cornwall, the North-west of Eng- 

 land, Scotland, and Ireland, are studied in chapter viii. Here we 

 see how greatly our knowledge of Ayrshire and Edinburghshire 

 has been advanced by the Geological Surveyors and others ; here 

 also we have the history and relationships of the Lower Silurian 

 schists, quartzites, and limestone of the Scottish Highlands clearly 

 explained, as well as the Silurian series of Ireland, and its relation 

 to the overlying Lower Devonian beds. 



The next two chapters are devoted to an illustrated systematic 

 account of the characters and distribution of the organic remains 



