Reviews—The South Wales Coal-field. O27 
the memoir, the one with and the other without the Boulder-clay and 
associated glacial sand and gravel. ‘The drifts do not very seriously 
obscure the sequence and structure in the Paleozoic rocks which 
form the foundation of the entire area, and the Drift map will 
therefore be most useful to geologists. The price of each map is Ls. 6d. 
The geological formations include the Upper Tremadoc of the 
Cambrian, the Ordovician from the Arenig to the Upper Bala, the 
Lower Llandovery of the Silurian, the Old Red Sandstone, and 
the Carboniferous rocks up to the lower part of the Pennant Grit. 
The general structure of the area is shown on sections printed on 
the margin of the map, and here we note that there is some incon- 
sistency in the nomenclature adopted, most of the divisions being 
indicated by their stratigraphical names, such as Tremadoc Beds and 
Redhill Beds, others by zonal (graptolitic) names. We think the 
term Arenig shales would have been better than Tetragraptus Beds 
from a practical point of view. 
A most difficult country is that in the northern part of the area, 
where the Lower Paleozoic rocks are folded, inverted, and faulted, and 
shales of different ages and sometimes of similar character are brought 
into abrupt contact; but the authors have thoroughly elucidated the 
geological structure by their careful and detailed researches in the 
field, by the collection of fossils, and with the aid of Dr. Ivor Thomas 
in the Museum at Jermyn Street, of Mrs. Shakespear in the deter- 
mination of the Graptolites, of Mr. P. Lake with regard to Trilobites, 
and of Dr. C. A. Matley with Brachiopods. Most of the disturbances 
affecting the Lower Paleozoic rocks took place prior to the deposition 
of the Old Red Sandstone, and between these groups there is 
everywhere great unconformity. 
Remains of Cephalaspis and Pteraspis are recorded from the Lower 
Old Red Sandstone; and some plant-remains, Artisea and Stigmaria, 
identified by Dr. R. Kidston, have been found in the Penlan quartzite 
near Kidwelly, a rock assigned to the Upper Old Red Sandstone. 
The complex zonal divisions in the Carboniferous Limestone Series are 
described, and attention is then directed to the Millstone Grit and 
Coal-measures, which occupy the south-eastern portion of the area and 
form the western part of the main South Wales Coal-field. A small 
tract of the less productive coal-field which extends into Pembroke- 
shire is shown on the western margin of the map. The details in the 
Lower Coal Series form the most important practical part of this 
memoir. There are also notes on various economic products, including 
lead-ore, silica-stone (used for making fire-bricks), building-stones, etc. 
Among Drift deposits the occurrence is mentioned of two patches 
of sand at an altitude of more than 500 feet above sea-level east 
of Eglwys-Cymmyn. A shaft was sunk in 1906 to ascertain the 
nature of the strata, and 30 feet of sand, loam, and gravel were 
penetrated. It is noted that the sand contains an assemblage of 
minerals almost identical with that which was determined by 
Mr. H. H. Thomas in the Lower Pliocene Sands of St. Erth and 
St. Agnes in Cornwall. No fossils were obtained from the Welsh 
strata, which may have been deposited during the Glacial Period. 
