Mineralogy and Geology. 265 | 
Memoirs of the Geological Survey of Great Britain and of the 
1 soe of Practical Geology. The Geology of North Wales, by A. C. 
ae , F.R.S., Local Director of the Geological Survey of Gr eat Britain. 
382 pp. "Bvo, with numerous plates, a map and sections. London, 1866. 
13s. in boards—In a brief introductory notice of this volume preceding 
_ the Preface, Sir Roderick Murchison says, “The Memoir upon the Geo- 
logical Structure of North Wales which is now published is, I consider, 
the most important work which has been issued by the Geological ris bi 
d ctor;” and w 
Ww 
earliest fossiliferous rocks of Wales, and with great fulness and exactness 
of description. There are 26 lithographic plates of fossils, besides sec- 
tions, and a beautiful colored geological map of Wales. In the summary 
at page 229, Prof. Ramsay gives the following statement respecting the 
lowest of i Silurian beds. 
“The chief object of this Memoir has now been accomplished, for I 
have described in detail the Cambrian and Lower Silurian rocks of Meri- 
equivalents of the Irish rocks at oy and ‘of the poe sa ond 
sandstones in the northwest of Scotiand described = Sir Roderick 1 ion 
chison., In Wales, however, we never | et to their base, w a *2 
clear, for reer Wales there seems to be conformity, and even a 
gradual passage from the Cambrian rocks - ye Lingula flags. The 
are, therefore, intimately related to eac rhaps, excep - 
separation by line and color 
# ges — _ ula i from 5.0 aby: a 6,000 feet thick where ele con- 
own, abo a of Trilobites of the genera 
pene ibe (4), Agnostus (5 5), oo us (7), a (C 
lai ; 
ermi- 
