REVIEWS. 
THE Grotocy or ANGLESEY. By Epwarp GREENLY. Memoirs 
of H.M. Geological Survey. Two volumes, 980 pages, 60 plates, 
17 folding plates, 346 text-figures. 1920. Price 3 guineas. 
GrotocicaL Map or AnaieEsny, scale 1 in. to mile. Colour-printed. 
Price 2s. 6d. 
JHE appearance of this map and memoir is an event of first-rate 
importance in British geology, justly comparable with the 
publication of the North-West Highlands memoir, of world-wide 
renown. The two have, indeed, much in common ; both result from 
the application of detailed large-scale mapping to regions prominently 
composed of ancient crystalline rocks, both formulate tectonic 
conceptions of great boldness and grandeur, and if the area of 
Anglesey be small, it may fairly be claimed to be more complex, 
less well-exposed, and to include a much greater variety of later 
formations. On the personal side, however, the present production 
stands apart from almost all its great predecessors in that it is 
substantially the work of one man, who single-handed and at his 
own expense has devoted more than twenty years of his life to its 
accomplishment. 
The memoir is divided into five parts. Part I comprises an intro- 
duction, a history of previous research, and a very complete 
bibliography. Both in spirit and method the author's treatment 
of the work of his numerous predecessors leaves nothing to be 
desired, his admiration of their achievements is patent, and he 
concerns himself less with the restatement of dead controversies 
than with the recognition of each worker’s contribution to our 
knowledge of the island. Part IJ, which occupies the remaining 
352 pages of the first volume, is devoted to the study of the “ Mona 
Complex ”’, this being the term bestowed upon the series of ancient 
metamorphic rocks which occupy some two-thirds of the surface. 
Part II, occupying most of the second volume, deals with the Jater 
formations, which include representatives of nearly every Palzozoic - 
system, an interesting set of Tertiary dykes, and widespread glacial 
deposits. Part IV is devoted to economics, and in Part V are 
gathered together a number of additional studies of the nature of 
postscripts, many representing important developments in the 
_author’s views on the Mona Complex during the progress of 
publication. Appendices give particulars and statistics of maps, 
specimens, and plates, while in a final supplement the author presents 
a connected account of his views on the metamorphism of the Mona 
Complex. 
In Parts II and HI the treatment is naturally stratigraphical, 
and has the advantage of a uniform plan. For each system a general 
account is first given. This commences, after a short introduction, 
