240 Correspondence — Mr» Senry Sicks, 



THE OLDEST FOSSILIFEROUS EOCKS OF NOETHEEN ETJEOPE. 



Sir, — I have read the paper by Professor Linnarsson in the last 

 dumber of the Geological Magazine with much interest ; but I fail 

 to see in it any facts stated which require that I should in any way 

 modif}'- the views there criticized. Indeed, I must claim the evidence 

 l)rought forward as tending strongly to confirm those views. As this 

 subject will be treated of fully in my paper, which is now being 

 published in the G-eol. Mag., I will here only refer to one or two points 

 which Professor Linnarsson seems to have lost sight of in his paper. 



1. If the Swedish area was submerged, as suggested by him, at as 

 early a period as the British area, there is no reason why it should 

 not have been depressed to as great a depth. That this could not 

 have been the case, however, is quite clear from the examination of 

 the faunas and the sediments. The average thickness of the sedi- 

 ments in the British area at the close of the Cambrian was at least 

 15,000 feet, and at the close of the Lower Silurian 30,000 feet. As 

 these are perfectly conformable sediments, it is certain that a depres- 

 sion of over that amount had taken place. The average thickness for 

 the same period in Sweden is scarcely over 1,000 feet ; hence if the 

 depression there was equal to that in Britain, the sediments there 

 b)efore the close of the Lower Silurian must have been deposited in a 

 depth of 29,000 feet of water. I do not think Prof. Linnarsson can 

 possibly mean that the Swedish fauna of that period was likely to 

 have inhabited a sea of that depth. The British and Swedish faunas 

 are in many respects alike, and indicate the presence at that time of 

 very similar conditions. And the reef-building corals so plentiful in 

 each area prove conclusively that the depth of water could not have 

 been very great. 



2. As to the resemblance between the Harlech and Menevian 

 faunas, it is not greater than what might naturally be expected in 

 groups succeeding one another. The likeness indeed is not greater 

 than between widely separated groups in the Silurian. Moreover, 

 no one will believe that the forms of life in the Menevian had not 

 earlier representatives, and which need not have differed from them 

 very greatly. Indeed, the large size and high state of development 

 of the Trilobites in the Menevian group prove conclusively to my 

 mind that this state could only have been attained through many 

 previous faunas of a similar type. Hence it is but reasonable to sup- 

 pose that the very earliest Cambrian fauna which could be discovered 

 would not differ greatJy from the Menevian, and moreover that these 

 forms of life were probably in existence before a single bed of the 

 European Cambrian rocks had been deposited, or even the waters 

 had encroached on the old pre-Cambrian European Continent. 



April, 1876. Henry Hicks. 



UNFADING INK. 



Sir, — "Would yon or any of your readers kindly tell rae of the most suitable and 

 durable ink for marking Chalk specimens. I have for the last eighteen years marked 

 them with common writing ink; but I now find that in a great number of cases the 

 writing is fast disappearing, and that I must soon re-mark them with something more 

 durable, if I can find it. 



Driffield, East Yorkshire, J. R. Mortimer. 



April lOth, 1876. 



