248 ANNUAL OF SCIENTIFIC DISCOVERT. 



be supposed to be due at the period preceding the deposition of 

 the crag. It might be safely supposed that the sea-bottom, at the 

 period of the crag, consisted of a shoal bottom of chalk, nearly 

 level on the eastern side of our area, while the same stratum rose 

 as dry land to a considerable elevation towards its central and 

 western portions. There was no evidence that the sea at the 

 crag period occupied any part of the present estuary or wash. It 

 was probable, on the other hand, that the chalk must have ex- 

 tended considerably to the westward of its present escapement. 

 Immediately upon the chalk of Thorpe, where the crag rested 

 upon it, was a thick bed of angular flints, which appeared to be 

 the accumulated result of the removal of the chalk intervening 

 between several successive layers. It was amongst these flints 

 that numerous bones, teeth, and tusks of mastodon and elephas 

 meridionalis and other mammalia occurred. His opinion was that 

 the chalk to which these flints were due was moved by erosion of 

 currents which were not strong enough to remove the flint. To 

 account for the bones found amongst flints there was the alterna- 

 tive that the chalk formed a land surface on which bones were left, 

 the flints being accounted for by subaerial solution of the chalk. 

 He inclined to Mr. Prestvvich's view. At any rate, the sequence 

 of events introduced the deposition upon the crag of a fine clay, 

 most probably formed in an estuary open to the Northern Ocean. 

 To this estuary whales had access, and there was much reason for 

 supposing that it was no other than the estuary of the Rhine and 

 of the Thames, and other rivers which formed tributaries to it. 

 The sides of this estuary next became dry land, so as to allow of 

 the growth of the forest upon the old muddy bottom. He was 

 inclined to think this desiccation cosmical, or at an}' rate as affect- 

 ing so large a portion of the earth's surface as not to have left any 

 traces of occurrence in local fauna, or appreciable undulations of 

 the strata. There was reason to believe that the elevated condi- 

 tion of the surface must have lasted for a long period, and it 

 seemed from the fauna of the forest-bed to have been synchronous 

 with a warmer climate than that which preceded or followed it. 

 It was probable that the forest-bed extended to the chalk land as 

 far as the subsoil of clay extended ; but it was not probable that 

 vestiges of it would be alwa3"s preserved. As the land continued 

 to sink lower and lower, the laminated strata of sands, clays, and 

 gravels would accumulate and extend westward, but the forest-bed 

 would not be preserved beneath them except at those levels where 

 it became submerged before the area communicated with the open 

 sea. The close relations of the laminated beds to the crag beds 

 in position would lead one to infer that the coast-line differed little 

 from the coast-line of the crags. The lower boulder clay over- 

 laid the laminated beds. But during the interval between them 

 the sea must have become much deeper, and involved in a system 

 of extensive tidal currents. Ice capable of transporting mineral 

 matter and depositing it at the bottom of the sea occurred under 

 two modifications, as icebergs and as coast ice. 



After glancing at the evidence of iceberg action towards the 

 close of the deposition of the lower drift, the formation of which 



