Geologists’ Association. 
133 
worked at Branksea 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 cbaracter, and 
mark a great cbange in the conditions of the land, from a valley in 
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 furthereast 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, 
ainounting 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 orgauized 
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 creature, I not only found that he relates the occurrence of simi- 
larly-bored wood 300 miles up the river Gambia, but distinctly 
States that there is a species which lives in fresh water. Therefore 
this supposed marine indication may be on bis 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 forrner 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 ; Callianasscs, which burrowed in 
the mud ; Calyptraa, 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 
