92 Correspondence. 



Mr. Godwin- Austen, is, that tlie Coralline Crag was not contempo- 

 raneous with the Black Crag. The Black Crag is an older deposit 

 of the Crag sea, which had its representative in Suffolk, and from 

 which first the Coralline (in but very small numbers), and then the 

 Eed Crag, has derived its sharks' teeth and Cetacean bones, as have 

 also the Yellow and Grey Crags of Antwerp, Though the con- 

 ditions of the deposition of the Coralline Crag differ greatly from 

 those of the Red Crag, it does not follow, without further evidence, 

 that they were conditions contemporaneous with those under which 

 the Black Crag of Belgium was deposited. 



I have ventured to make these few observations, in relation to the 

 views of so eminent a geologist, chiefly with the desire that some one 

 may offer a better answer to my questions. 



Very truly yours, 



E. Eay Lankester. 

 Chkistchurch, Oxfoed, January 11, 1866, 



THE LOWER CAEBONIFEROUS EOCKS OF NORTH WALES. 

 To the Editor of the Geological Magazine. 



Dear Sir, — In connection with this subject, it may interest Mr. 

 Green and others of your readers if I subjoin an extract from a paper 

 on the " Mountain Limestone of North Wales," read by me before 

 the Oswestry Field-club, on June 4, 1861, and published in the 

 proceedings of that Society. 



" The Yoredale series, which, in Yorkshire, presents an alterna- 

 tion of beds of shale, limestone, sandstone, and coal, is not repre- 

 sented in North Wales, unless we regard the uppermost beds of lime- 

 stone and shale and the lowest fossiliferous layers of Millstone-grit 

 in our neighbourhood as occupying the same horizon, viz,, lying be- 

 tween the limestone proper and the coarse and unfossiliferous grits," 



Such was the suggestion I offered nearly six years ago, still I 

 think it would be unwise to interfere with the nomenclature of the 

 " Survey" in this respect, especially since the change in North Wales 

 from calcareous to arenaceous matter is much more sudden and per- 

 manent than it is further north, and also while some Mountain Lime- 

 stone fossils extend from the base of that formation to the top of the 

 grit, yet at varying horizons along the belt these become associated 

 with plants and other fossils of the Coal-measures. I would also 

 observe that the top coarse beds of Mr. Green's section are very local 

 in their occurrence, and give place in the neighbourhood to those of 

 a much finer texture. — I am, Sir, yours truly, 



D. C. Davies. 

 CoNEYGEEEN HousE, OswESTEY, January 11, 1867. 



