The Building of the British Isles. 319 



as the uplift of the whole British area at the end of the Cretaceous 

 doubtless formed a series of consequential rivers, which flowed across 

 Britain from the western uplands to the North Sea. So far all British 

 geologists agree with Professor Davis, whose paper discussing the 

 relics of that primitive arrangement of our rivers must be regarded as 

 a most important contribution to British geographical evolution. The 

 chief difference of opinion is as to the date at which this system was 

 destroyed. Mr. Jukes-Browne regards the Severn as a very ancient 

 valley, whereas according to Professor Davis it is relatively modern. 

 The plan of the existin g rivers of Central and Southern England seems 

 to result from a radial drainage from the Midlands. I called attention 

 to some evidence in favour of this view in a paper on the Evolution of 

 the Thames published in 1894 ; but that paper was incomplete, as it 

 offered no explanation and cited no other evidence for the hypothetical 

 central plateau, which the radial arrangement of the rivers seemed to 

 indicate as having existed in Lower Cainozoic times. An area of 

 highland might have been left there, owing to the more rapid 

 subsidence of the land to the east and south ; the Midlands might 

 have been supported by the same ridge that had earlier caused the 

 difference between the north-eastern and south-western types of the 

 Lower Oolites. But for that supposition I knew of no direct evidence. 

 Dr. Strahan and Mr. Jukes-Browne have now established an uplift of 

 this area which would have served as the original feeding- ground of 

 a radial system of rivers; these authors differ somewhat as to the date 

 of the uplift, Dr. Strahan regarding it as Miocene and Mr. Jukes- 

 Browne as Eocene. According to the latter view the Severn would 

 be a very ancient river, and much older than the Thames. 



In connexion with this question it is interesting to note the author's 

 view regarding peneplanes, a spelling which he accepts as the more 

 correct form of the word. He emphatically dissents from Professor 

 Davis' view that peneplanes are due to subaerial action ; he remarks 

 that this "may be a theoretical possibility, but I think it has very 

 seldom, if ever, been accomplished" (p. 425). That some peneplanes 

 may be remnants of plains of marine denudation is quite probable ; 

 but it seems to be generally admitted that the formation of peneplanes 

 by the combined action of river and wind is one of the most widespread 

 of geographical processes. 



In a book of so wide a scope and dealing with so scattered a literature 

 there must be omissions and points where opinions differ. Thus, the 

 statement (p. 454) that marine mollusca do not occur above the height 

 of 500 feet in the Scottish glacial deposits shows that the author has 

 overlooked Smith's excellent memoir on the Ayrshire drifts; the terms 

 Bryozoa and Polyzoa are used indiscriminately (e.g. pp. 321-4). 

 The author occasionally refers (as on p. 360) to dykes as lava-filled 

 fissures, a practice which was once common among miners, but which 

 they have fortunately learnt to avoid. 



The author is conservative in the classification of some systems, 

 such as the Silurian; and where he is less so it would have been 

 useful if he had given some explanation or reference when he adopts 

 a well-known term in a special sense, as in the use of Cenomanian for 

 the Lower Chalk. Mr. Jukes-Browne is severe on the retention of 



