REVIEWS. 
TRE GEoLoGy oF THE SouTH WaLEes CoaLrreLpD. Part XIII: 
THE COUNTRY AROUND PEMBROKE AND TENBY. Being an 
account of the region comprised in Sheets 244 and 245 of the 
map. By H. KH. lL. Drxon, B.Sc., F.G.8. Memoirs of the 
Geological Survey. pp. i-vi, 1-220, with 5 plates, 12 maps, and 
1 section. 1921. Price 8s. net. 
felts memoir concludes the series devoted to the description of 
the maps of the revised survey of the South Wales Coalfield. 
The introduction contains an admirable account of the physical 
structure of the area, and is fcllowed by a detailed account of the 
rocks in the order of their formation. The Lower Paleozoic rocks 
are found in two important anticlines. Upper and Lower Llanvirn, 
Wenlock, and Ludlow formations are represented, those of Silurian 
age being of the type characteristic of South Wales. 
The Devonian rocks are of great interest. Both Lower and Upper 
Old Red Sandstone occur, the former with Pteraspids, the latter 
with Holoptychius. The upper beds are discordant to the lower. 
In the upper group occur the Skrinkle beds, an interbedded marine 
and continental series. These Skrinkle beds were briefly noticed 
in the memoir of the country around Milford in 1916, but full details 
appear in the present memoir. The marine fauna agrees with that 
of the Baggy beds, and the containing rocks are, therefore, as 
surmised by Salter, of Devonian age, even if, as seems to be the case, 
the Pelton beds must be removed to the Carboniferous system 
The Lower Carboniferous heds apparently show a complete 
succession from “ K ” to “D3”. The description is based upon the 
classification of Vaughan, whose labours in these rocks have been 
so successfully taken up by the author of the memoir, and the account 
of the rocks is of the utmost importance to students of the system. 
‘“ Reef-structures ”’ are described in the division C, and the author 
appears to favour their contemporaneous origin. The Upper 
Carboniferous rocks are almost entirely referable to the Millstone 
Grit, a small patch of Coal-measures appearing only at the northern 
border. The lower part of the Millstone Grit series contains the well- 
known Radiolarian cherts, and a fauna of part of the Pendleside 
series. The highest beds have yielded a Westphalian flora. 
Of Mesozoic rocks no true deposits are found, but some remarkable 
“ gash-breccias’’ are almost certainly of Triassic age. They are 
regarded as due to collapse and infilling of cavities eroded by under- 
ground waters. 
Certain pipe-clays at Flimston are considered as being of Tertiary 
age, and probably the equivalent of the Bovey Tracy beds; while 
certain gravels with quartz pebbles may be relics of Phocene river- 
deposits. - 
A very important chapter is devoted to tectonics. Evidence is 
given of many periods of earth-movement, greatest stress being laid 
