﻿Geologists' Association. 133 



worked at Branlcsea below the sea-level, at Parkstone, and near 

 Bourne. At Alum Bay they are tilted up, and are full of beautiful 

 fossil leaves. (See Woodcuts Figs. 3 and 5.) 



The series of beds above are of a different character, and 

 mark a great change in the conditions of the land, from a valley iu 

 which the previous beds were deposited, to a broad low-lying tract 

 in proximity to the sea. We believe we can trace how this tract 

 became gradually lowered and lowered down to the sea-level. 



The conclusion as to the gradual lowering of the land in this 

 area is borne out by the fact that in the cliffs near Poole, which are 

 slightly lower in position than those farther east, we get only leaves 

 of evergreens and forest trees, whilst as we work our way east so 

 as to meet with beds on a higher level, or, which is the same thing, 

 of more recent age, we get a mixture of ferns and other plants, 

 which require much moisture ; whilst further east still we get assem- 

 blages of plants that could only have lived in absolute swamps. 



Low as the land appears to have become, we have no evidence 

 whatever, throughout the whole thickness of this part of the series, 

 amounting to 300 feet at least, with one exception, that it was low 

 enough to be inundated by the sea, as the few shells that have been 

 found are of fresh-water kinds. The exception is the occurrence of 

 logs of wood bored by the Teredo. All the ship-worms generally 

 known to us live only in salt water, and are so delicately organized 

 that the slightest mixture of fresh water instantly kills them. This 

 isolated fact for some time presented a grave difficulty ; but happen- 

 ing to read Mr. Gwyn Jeffreys' interesting account of the habits of 

 this cx'eature, I not only found that he relates the occurrence of simi- 

 larly-bored wood 300 miles up the river G-ambia, but distinctly 

 states that there is a species which lives in fresh water. Therefore 

 this supposed marine indication may be on his authority removed, 

 and, supposing this theory should be verified and accepted, we may 

 safely infer that these middle beds are of fresh-water origin. 



We now come to the third series of beds. A still continued sink- 

 ing of the area brought this swampy condition so low that the sea 

 was no longer kept out, but, bursting through, formed great salt- 

 water lagoons teeming with life ; for we suddenly find crowds of 

 marine forms imbedded in what was formerly black mud. 



In this series of marine beds we have at the bottom lagoon beds, 

 as I call them, indicating the former existence of mud-banks left dry 

 or shallow between each returning tide. We still find here leaves 

 of trees, many of them doubtless overhanging the lagoons, which 

 have so slowly decayed, that they are overgrown with Polyzoa; 

 crowds of oysters are met with ; we find the remains of shore-crabs, 

 which overran the muddy shore ; Callianassce, which burrowed in 

 the mud ; Calyptrma, Area, Corbula, and many other shell-bearing 

 molluscs. This lagoon condition went on until the gradual sink- 

 ing permitted the ever-encroaching surf to break over the lagoon 

 barrier, to rush in and overwhelm them with rolled shingle and sea- 

 sand. We still trace the lagoon condition for a mile or so east, 

 where it is represented by cigar-ash-coloured sands, impregnated 



