RECENT ADVANCES IN SCIENCE 209 



height of 430 feet against the Snowdon mountains (Geol. Mag. 

 191 8, 5, 145-57). Pre-glacial erosion has sculptured this 

 plain into a region of hills and valleys which has its own 

 drainage system independent of that of the mountain system 

 adjoining it. A similar plain, believed to be not more recent 

 than Pliocene, occurs in Cornwall and Devon at the same 

 height. The evidence indicates that these plains were formed 

 contemporaneously by marine erosion. 



Prof. P. F. Kendall discusses in detail the origin of the 

 splits in coal seams, especially the type in which a lense of 

 dirt or sand with an arched roof and flat floor is intercalated 

 in the coal. He ascribes these to the deposition of sediment 

 along a stream channel in the original peat, covered later 

 by a second layer of peat. In the subsequent contraction of 

 the strata upon consolidation, the peat, being much more com- 

 pressible, shrinks far more than the enclosed mass of sand, 

 which, as shown by diagrams, must assume the form of a 

 plano-convex lens with the convexity upwards. In the specific 

 case of the Silkstone seam of Yorkshire the split in the seam, 

 when mapped, occupies a long sinuous track like that of a 

 meandering river — a fact which offers valuable confirmation 

 of the ingenious theory put forward (Trans. Inst. Min. Eng. 

 191 8, 54, 460-79). 



Stratigraphical and Regional Geology. — The Presidential 

 Address of Dr. A. L. du Toit to the Geological Society of South 

 Africa records the advances that have been made in the last 

 fifteen years towards the elucidation of the detailed strati- 

 graphy of the Karroo System (Proc. Geol. Soc. S. Africa, 191 8, 

 xvii-xxxvi). The Karroo occupies one half of the total area 

 of the Union of South Africa ; it has at its base the greatest 

 Palaeozoic glacial formation yet known ; it is capped by a 

 thick series of lavas and penetrated by a series of basic sills 

 and dykes on a scale probably unsurpassed in any part of the 

 world. In time it ranges from the Upper Carboniferous to the 

 close of the Triassic, and was deposited under continental 

 conditions upon the ancient Gondwana land mass. Its de- 

 tailed investigation is therefore of great scientific interest, 

 especially as it is also the source of South Africa's mineral fuel. 



Dr. G. Hickling has compiled an excellent summary of the 

 geology of Manchester as revealed by recent boring data 

 {Trans. Inst. Min. Eng. 191 8, 54, 367-417). He shows that 



