380 Correspondence — Mr. Henry Hicks. 



he gone over the papers still more carefully. In the paper first 

 referred to I stated that in all the areas the first sediments thrown 

 down on the old Pre-Cambrian land were either conglomerates, grits 

 or sandstones, and which, being for the most part the result of a 

 rather sudden encroachment of the sea on land, on which there was 

 probably an abundance of loose material, would be heaped up rapidly. 

 A period of rest would probably follow this rather sudden encroach- 

 ment, and for a while fine sediments would be thrown down, not 

 necessarily as the result of a very deep sea, but because all material 

 would be washed ofi" the exposed parts, and marine erosion on the 

 hard rocks would yield but little sediment. In the Welsh areas we 

 have evidence of several such successions in the sediments even in 

 the Lower Cambrian epoch. The finer deposits being separated from 

 each other sometimes by great thicknesses of sandy or gritty materials, 

 showing the depression to have been great, and that a large land 

 surface had probably been then submerged. From this it is clear 

 that each depression would cause the first areas submerged to become 

 more and more oceanic, and that each area also at one time or other 

 must have been a shore-line. The fine sediments in the British area 

 are of enormous thickness compared with those in Sweden, and that 

 they were not heaped up rapidly is certain from the fact that the 

 range of the species contained in them is often very limited indeed. 

 The following table of the Lower Cambrian rocks will clearly show 

 the several changes which took place at that time in the Welsh area, 

 and the succession of the faunas : 



Lower Cambbiais". Thickness in feet. 



1. Conglomerates 60-200 



2. Greenish flaggy Sandstones .„.. 460 



3. Eed fine-grained Shales or Slates affording the earliest traces of 



organic remains, viz. Lingulella, Discina, LepercUtia, etc 50 



4. Purple and greenish Sandstones 1000 



5. Yello-wish-grey Sandstones, Shales and Flags, containing the genera 



Flutonia, Conocoryphe, Microdiscus, Agnoslus, Faradoxides, Theca, 

 Protospongia, JDiscina, Obolella, Lingulella 150 



6. Grey, purple and red Sandstones, alternating with Slates and Shales 



containing most of the above-mentioned genera (mostly new species) 1500 



7. Grey flaggy beds containing Faradoxides Aurora^ Conocoryphe hiifo^ etc. 150 



8. The true beds of the "Menevian Group," for the most part calcareous 



Flags, Slates, and Shales, richly fossiliferous throughout, but chiefly 



in zones ...., 600 



Now, the only species which probably is common to the British 

 and Swedish faunas in the Lower Cambrian rocks is Paradoxides 

 Fordihammeri [Hicksii, Salter), and as this occurs high up in the 

 Menevian group, and as each Paradoxides also has but a short 

 range in the group, it seems reasonable to think that the Para- 

 doxides schists in Sweden do not represent at the most more than 

 the Menevian group. Hence, as there is no evidence of a previous 

 fauna, it appears clear to me that this was the first fauna in that area 

 after the first encroachment of the sea, for we have but one series of 

 sandstones, and these are ripple-marked, showing shore conditions. 

 If Prof. Linnarsson could but be brought to recognize this view of 

 the gradual encroachment of the sea from a western or south- 

 western direction over the European area, I am certain he would 



