286 Correspondence. — Mr. Sugli Miller, 



and before the Middle and Upper ; and a paragrapli to this effect 

 was inserted in the Introduction to the Crag Mollusca Supplement 

 by Mr. Harmer and myself, which is published in the volume of the 

 Pala3ontographical Society for 1871. 



"With reference to the observation that all the great features of 

 the country had come into existence before the Glacial period, I have 

 already explained that several years ago I saw, and stated, that such of 

 those great features as are connected with the curvilinear escarpments 

 were of pre-glacial origin. What I have long contended for against 

 the general opinion of geologists, and still contend for, is that such 

 of these great features as are connected v^th the rectilinear escarp- 

 ments and ridges of the south and south-east of England, as e.g. 

 those of the Isles of Wight and Purbeck, and of the Portsdown and 

 Hogsback hills, are not of pre-glacial origin ; but that they origi- 

 nated at the close of the Glacial period, or rather at what I call 

 earliest post-glacial, i.e. at the commencement of the emergence, as 

 explained at page 21 of my paper in the Quarterly Journal, read 

 Nov. 9, 1870. 



" It would, I think, save much misapprehension and confusion, both 

 now and in future, if you could manage to have this letter of expla- 

 nation inserted at the end of your paper (if it is printed), and before 

 the report of the discussion upon it. Seaeles Y. Wood, Jun. 



'' W. H. Penning, Esq." 



GLACIAL OEIGIN OF LAKE-BASINS. 



Sir, — It appears to me that stratigraphical evidence can most 

 successfully dispute the verdict of "not proven" brought by Mr. 

 Judd against Prof. Ramsaj^'s theory of the glacial origin " of certain 

 lakes." That subsidences of the crust can produce rock-basins is 

 affirmed both by historical and geological evidence ; but if the 

 basins chance to lie among strata so regular and well exposed that 

 the fact of subsidence coald not have failed to record itself, and if 

 the outcrops on \hQ contrary tell only of erosion, theories of sub- 

 sidence are fairly out of court ; and it remains only to fix on the 

 erosive agent. 



The outcrop of the Carboniferous rocks of West Northumberland 

 is so marked and regular, that on the Ordnance one-inch map the 

 shading is disposed in bars alternately dark and light, representing 

 linear escarpments with their interspaces ; and among these, which 

 may be said to dip at from 6° to V2P. and are clearly pre-glacial, lie 

 rock -basins known as the " Northumberland lakes." Obviously, if these 

 were occasioned by localized subsidence, deviation from the average 

 line of strike must have ensued in the beds, while concentrated erosion 

 would leave an excavated outcrop not attended by any such change. 

 By careful and repeated observations, I find the latter to be the case. 

 Tracing the scarped outcrop towards the water, those on the dipivard 

 side of the basin are scooped back into a crescentic curve, those 

 more central to it being obliterated altogether. No facts can be more 

 certain than that (1) subsidence would have altered the dip ap- 

 preciably, and that (2) it has not done so ; but by simply projecting 



