Sir IT. Howorth — Recent CJianges of Level. 405 



this is particularly marked, for immediately below the lowest 

 Paradoxides zone a fine conglomerate containing angular fragments 

 of volcanic material occurs, and this I have taken as the boundary 

 line between the Caerfai (Olenelliis beds) and the overlying Solva 

 (Plutonian and Paradoxides beds). Again, at the top of the 

 Menevian, and separating it from the overlying Lingula flags 

 (Olenus beds), massive grits succeed black slates, and in these grits 

 we again meet with volcanic materials. Were it not for these 

 changes I doubt not the genera would have a gi'eater vertical range, 

 and at certain horizons also intermediate forms would be found. In 

 naming groups of strata after a genus there is, of course, the danger 

 that the pi'evailing genus in one area may not be so in another, and 

 may indeed be entirely absent, though the beds may be of exactly 

 the same age. Still, as already stated, other associated fossils are 

 usually equally characteristic of the zone, therefore there is not, 

 as a rule, much difficulty in defining the horizon even when the 

 stratigraphical evidence is incomplete. In Wales there are many 

 exposures of Lower Cambrian rocks which would be likely to yield 

 fossils to a careful seai'ch, and I feel confident that, ere long, they 

 will yield a much richer fauna than has hitherto been obtained 

 from them. 



{To he continued.) 



IV. — The Most Eecent Changes of Level and their Teaching. 

 The Rapid Collapse op Some Districts at the Close of 

 the Mammoth Age. 



By Sir Henry H. Howorth, K.C.I.E., M.P., F.R.S., F.G.S. 



IN some recent papers published in the Geological Magazine, 

 I have endeavoured to show that at the close of the Mammoth 

 age there was a very considerable dislocation of the earth's crust, 

 and that a consequence of it was the upheaval of some of the 

 highest masses of land on the earth, including the massive 

 mountains of Asia and the American Cordillera. I now propose 

 to show that (as is a priori probable) there was a concurrent 

 collapse or sinking of the ground over large areas, which, as in the 

 corresponding upheaval, was very rapid, if not sudden. 



We will begin with our own latitudes. There cannot be any 

 doubt that in the Mammoth age England was joined to the Continent. 

 This, I presume, is accepted by everybody. We cannot account for 

 the presence here of the Pleistocene and existing Mammals by 

 any other postulate than the existence of a land-bridge when the 

 Mammoth and the Tichorhine Ehinoceros were living on both sides 

 of what is now the Channel. 



This is plain. Where was this bridge? Was it a continuous 

 stretch of land entirely occupying the English Channel, as has 

 been generally supposed, and as has in consequence been figured 

 on many maps ; or was it a much more partial one, forming an 

 isthmus. In my view there can be little doubt it was the latter. 

 In the great headland at Selsea, Godwin-Austen has described large 

 portions of the skeleton of a Mammoth as found mixed with 



