306 Notices respecting New Books. 



Table II. The approximation of the figures in the second and 

 third columns is seen to be extremely close. 



Throughout this investigation I have been efficiently assisted 

 by Mr. W. F. Barrett, whose rapid progress in scientific know- 

 ledge and experimental skill during the three years that he has 

 assisted me has given me great satisfaction. 



XXXIX. Notices respecting New Books. 



Memoirs of the Geological Survey of Great Britain. Vol. III. — The 

 Geology of North Wales. By Professor A. C. Ramsay, F.R.S., 

 Local Director of the Geological Survey of Great Britain. With an 

 Appendix on the Fossils ; by J. W. Salter, A.L.S., F.G.S., late 

 Palaeontologist to the Survey. London : Longmans. 8vo. 381 pp., 

 with Maps, Sections, and 26 Plates of Fossils. 



13ERHAPS no long-deferred publication has ever been looked for- 

 ward toby geologists with such a continuous and well-sustained 

 expectation as the memoir now before us. The delay in its appear- 

 ance has no doubt tended to render it more complete than it would 

 otherwise have been ; and we must now recognize it as being by far 

 the most complete exposition yet published of the Geology of North 

 Wales. 



Necessarily the memoir is chiefly descriptive, the principal design 

 being to give " such a detailed description of the Silurian rocks of 

 North Wales, that any one may ascertain the structure of any minor 

 area in which he may be interested." This description occupies the 

 bulk of the work ; but it is prefaced by a general sketch of the Geo- 

 logy of Wales, to which we must especially draw attention. 



The physical relations of the older rocks possess more general in- 

 terest than the peculiarities of structure and extension of any one 

 division ; and Professor Ramsay has therefore judiciously given a 

 brief description of them, being the result of a multitude of careful 

 observations wherever Silurian strata occur in Britain. We thus 

 learn that " there is no sign of unconformity anywhere between the 

 Cambrian rocks and the overlying Lingula-flags of Merionethshire, 

 Caernarvonshire, and the Longmynd ; " but that there is probably 

 an unconformity between the Tremadoc slates and the Lingula-flags 

 beneath. The Llandeilo flags, which come next in the series, are 

 also in all probability unconformable to the Tremadoc slates ; for 

 " in Anglesea strata of Llandeilo and Caradoc age lie directly on 

 Cambrian rocks, showing so great and rapid an overlap of the Lin- 

 gula and Tremadoc series, that it seems to indicate unconformity 

 between these black slaty strata and the Tremadoc and Lingula-beds 

 below." 



The lower Llandovery strata appear to be conformable to the 

 Bala or Caradoc beds, which are themselves conformable to the Llan- 

 deilo rocks ; hence the Geological Survey have retained the lower 

 Llandovery strata in the Lower Silurian division, while the upper 



