90 KEPOKT — 1872. 



GEOLOGY. 



Address hy Eoeeet A. C. Godwin-- Austen, F.R.S., F.G.S., ^r., 

 President of the Section. 



The Geological Section is fortunate in respect of this year's place of meeting' of 

 the Britisli Association. The county of Sussex presents a -wide range to the g-eolo- 

 gical observer : there is the great freshwater Wealden series, next the entire Cre- 

 taceous gi'oup, then portions of the Nummulitic gi'oup, including the nnique fossili- 

 ferous beds of Braclilesham ; at Selsey is to be seenla remnant of a definite Tertiary 

 period, of which at no other place in England is' there any record ; lastly, the 

 evidence as to local conditions during the Glacial period is peculiarly interesting. 

 This rich field has not wanted competent labourers, foremost amongst whom must 

 be named Ur. Gideon Mantell, who in his day did so much by his zeal and know- 

 ledge to diifuse a taste for his favourite pursuit. There must also be added the 

 names of Mr. Martin, of Pulborough, and Mr. Dixon, of Bognor. 



It might perhaps be a fitting preliminary to the local communications whicli wo 

 may expect in the course of this fleeting, should I here give a summary of what has 

 been already done with reference to the geology of this South-east of England ; but 

 to many who meet now in this Section, very much of such a survey would be 

 Himiliar. Instead of this I propose to call attention to what is the peculiar feature 

 of our local geology— namely, its great AVealden formation, the product of that vast 

 lake or sound which, at a time before a particle of tlie chalk hills of Sussex had 

 been formed, covered an area larger than the whole of the South-east of this island. 

 What I shall eudeavom- to put before you, a point not generally understood, is with 

 reference to the place of formations akin to our Wealden in the records of past 

 time, to enable you to realize what were then the geographical conditions of the 

 northern hemisphere, what the distribution and extent of other areas of fresh 

 water, the equivalents of our Wealden. 



Thicc of the Fresh- and Brackish-water Formations on the Geological Scale, 



When a general view is taken of the successive physiographical conditions of by- 

 gone geological periods, it is seen in respect of each, such as those of the Pala?o- 

 zoic period or of the Mesozoic, of the Jurassic, Cretaceous, and Nummulitic, 

 which all represent distinct periods of past time and are all the products of 

 purely marine conditions, that what is at present terrestrial sru'face was at those 

 times to a great extent covered by water, and that the great geological formations 

 are merely old sea-beds. 



When on a projection of the northern hemisphere the known extent of each of 

 these old seas is represented, as on the maps exhibited, it is also seen to how 

 great an extent, at those times, the area of water exceeded what it is at present ; 

 at each of these great periods the northern hemisphere must liave presented just 

 such a preponderance of water as the southern hemisphere does at. present : 

 and it is further to be remarked how closely the area of one period of northern 

 geological submergence corresponds with the others, as the Nummulitic with tho 

 Cretaceous, and tlie Cretaceous with the Jurassic. Whatever the cause, there is to 

 be seen in this a recurrence of like conditions at enormously long intervals of time. 



If next the internal evidence to be derived from these Mesozoic formations be 

 taken, it is to be seen, as is familiar to most geologists, that each, when most com- 

 plete, presents a like order of change from its older to its newer portions. 



Over the mid-European area, shallow-water accumulations, such as shingle 

 and sand zones (infra- Liassic), preceded the deeper-water shales and limestones of 

 the Lias. Jurassic Oolites follow upon these, indicating somewhat decreased depths 

 for tlie Middle Jurassic series. Oscillations of surface mark this period ; and with 

 respect to its physiogi-aphy, Mr. Darwin has given his opinion that ihe Malay 

 archipelago, with its numerous large islands separated by wide and shallow seas, 

 probably represents the former state of Europe, when the Middle Jurassic beds 

 were accumulating. Next follow deep-water depositions, when the widely spread 

 liimmeridge series was formed, ending upwards with the Portland beds. 



