Tojpley — Physical Geography of East Yorkshire. 439 



of Loch. Tay runs along tKe top of an anticlinal arch. Hence that 

 which in geological structure is a depression, has by denudation 

 become a great mountain, while what is an elevation has been 

 turned into a deep valley." Mr. Wbitaker informs me that detached 

 hills in the London Tertiary country have very commonly this in- 

 ward dip ; so too have the Tertiary hills west of Canterbury. 



I venture to call the attention of geologists to this generally 

 hasined or synclinal forms of detached hills. There is no reason, if 

 hUls and valleys are due to marine action, why the hills should be 

 synclinals and the valleys sometimes anticlinals, since the sea where 

 we now see it at work pays no regard to dip and strike. 



PosTSOuiPT. — Although not immediately bearing upon the district 

 described in the foregoing paper, I should like to call attention to a 

 work by Mr. William Wallace,^ in which the structure of the Alston 

 Moor district, and the Tyne valley generally, is described. The 

 author clearly recognises the power of rain and rivers in excavating 

 valleys, and also that marine action had previously, and during the 

 upheaval of the comitry, largely denuded the beds. I subjoin a few 

 passages from this interesting work (pp. 45, 48) : " It is difficult 

 to resist the inference that the bed of the Tyne river above Alston 

 must have been some 200 feet higher than at present." " There are 

 less clear indications of its having occupied still higher positions." 

 " As the river deepened its channel, and the sides of the hills were 

 decomposed and carried away by pluvial agency, all marks of 

 ancient river beds must have been destroyed." " . . . . the sheets 

 of strata, which, once stretched from the more elevated sides of the 

 mountain across the valleys far above the bed of the present stream, 

 were gradually removed by the action of the waves and currents 

 of the sea ; and further, that previously the strata had been thrown 

 out of their original horizontal position, the erosion being regulated 

 by those portions which, were most elevated, as the range of the 

 Pennine mountains, and by the anticlinal axis stretching from the 

 summit of Cross Fell to the sources of the Tyne, and from there 

 north-eastwards to Kilhope Law. The exact point, however, where 

 breaker action ended, and the erosive action of the streams now 

 flowing in the country began, is not, perhaps, determinable." 



ni. — Notes on the Compakative Structuke of Surfaces prodtjced 



BY SUBAERIAL AND MaRINE DeNXJDATION. 

 By George Maw, F.G.S., etc. 



THE article by Mr. Mackintosh on " The Cliffs, Gorges, and 

 Valleys of Wales," in the September number of the Geological 

 Magazine, raises so many questions in opposition to the views I en- 

 deavoured to support in the previous number, that I venture to offer 



1 "The Laws wMch regulate the deposition of Lead Ore iu Veins." 8yo. 1861 

 Chap. ii. " Elevation of the Strata and Denudation of the country." 



