the Purbeck and Wealden Deposits of England and France, 281 



mixed with lime, and in some parts, and particularly during the 

 earlier period of the lower greensand formation, with argillaceous 

 material ; but at the point when the palaeozoic barrier reached the 

 water's edge, forming an extensive reef rising in parts into islands, 

 the degradation of such shale as that brought up by the borer at 

 Harwich, taking place over an extensively shallow area, furnished 

 the dark aluminous silt that forms so marked a feature in the 

 gault of the South-east of England, and was deposited over and 

 around that barrier. As the depression proceeded uninterruptedly, 

 the stages of sand, marl, and pure chalk successively occur over 

 the region, marking the increasing stages of depth until some- 

 thing approaching to oceanic depth was reached, when the flint- 

 layers grew. 



In the paper before referred to, I attempted to show that the 

 geological movements of the mesozoic period, up to the end of 

 the oolitic age, were due to several great systems or bands of 

 volcanic action in different parts of the earth, which possessed a 

 direction coinciding more or less with the meridians of longitude, 

 the effect of which was to produce a trend of the land generally 

 from north to south; and that it was to one of these bands, 

 which I designated as the system of Portugal prolonged into 

 England, that the continuous elevation of the Jurassic gulfs 

 of England and France, which lay on the eastern side of the 

 band, was due. I also pointed out that the period of depres- 

 sion which succeeded this commenced (in Europe at least) 

 during the lower cretaceous epoch, and was marked by a total 

 change in the direction of the volcanic action from the direction 

 of north to south which had prevailed since the commencement 

 of the Permian age, to one from west to east, a direction which 

 indicated, with very few exceptions, the prevalent one of all systems 

 originating since the lower cretaceous epoch. The commence- 

 ment of this total change I regarded as marked by the formation 

 of the system of the principal part of the Pyrenees, which, 

 according to M. d'Archiac, originated towards the close of the 

 lower cretaceous epoch*. Now the mode in which the subsi- 

 dence of theAnglo-Frankish basin took place during the formation 

 of the Wealden deposit, seems to me well to illustrate some of 

 the effects which this total change in the direction of the volcanic 

 action produced. Thus, while the elevatory action of the oolitic 

 age over the north-west of Europe was due to a line of volcanic 

 action of which the direction may be indicated by the seventh 

 meridian of longitude, extending from the Portuguese frontier to 



* If M. Coquand's view, that the lower cretaceous deposits are absent in 

 the Pyrenees equally as in the Charentes, be correct, it would seem that the 

 origin of the Pyrenean system must be advanced to a later part of the cre- 

 taceous age than that assigned to it by M. d'Archiac. 



