44. REPORT—1845. 
but no proof has yet been given that it is of the same date or exactly of the same 
origin, and therefore the author gives it its local and provincial name. It is of con- 
siderable but very irregular thickness, of which 200 feet may be stated as about the 
maximum for the country near Cambridge. In general its thickness is much less, 
The higher table-lands on the confines of Cambridgeshire, Bedfordshire and Hunt- 
ingdonshire, are almost entirely composed of it; but it is found also at lower levels, 
and sometimes immediately under the marsh lands. It contains innumerable peb- 
bles and fragments of chalk, and multitudes of septaria and other stony concretions 
drifted out of the great fen-clay. Entangled in its mass are occasionally found blocks 
of greensand, several tons in weight, and driven several miles from the parent rock, 
The author affirms his conviction that ninety-nine parts out of a hundred of the 
whole mass are derived from the country of the great fen-clay. Icebergs may, during 
the period, have transported boulders from a great distance, and dropped them among 
the superficial deposits of the country. But no conceivable action of icebergs could 
have scooped out the great hollow of the fens and spread the materials, far and wide, 
over all the higher lands on the south-east side of the great level. ‘The brown clay 
has been pushed bodily onward by the propelling force of water, the propelling force 
having been probably brought into action by some sudden elevation and change of 
level between land and water, of which the faults above noticed may give a partial 
evidence. In this neighbourhood there are no old local freshwater deposits above the 
brown clay like those which have been noticed on the coast of Norfolk, 
2. Flint Gravel.—This generally occupies the low country, and is too well-known 
to need description in this sketch. Its level is however by no means constant, and 
as it sometimes contains blocks of stone brought from a great distance, the author 
refers it to the ill-defined period when the great erratic blocks were transported over 
so many parts of England. That it was mainly produced by the action of the sea 
during changes of level, cannot admit of doubt; but in a few places (e.g. near Barn- 
well) its finer sandy beds contain many well-preserved specimens both of land and 
freshwater shells, most of which are of existing species. It is conjectured that these 
shells may have been chiefly derived from old freshwater deposits (like those of Nor- 
folk) which existed, here and there, on the surface of the brown clay, at the time 
the flint gravel was in progress of formation. The facts at any rate are interesting ; 
and in the finer beds of gravel near Barnwell, these shells are found associated with 
drifted mammals’ bones of many species, most of which are extinct, e. g. Mammoth, 
Rhinoceros, Hippopotamus, gigantic Bos, Equus, &c. This association of fossils 
is described in a paper by the Rev. T. B. Brodie, in the ‘Cambridge Transactions,’ 
and the same fact was noticed twenty-five years since in a communication by 
J. Okes, Esq. 
Modern Deposits connected with the present Drainage of the Country. 
The towns and villages upon the great level are generally built on hummocks of 
the brown clay, or on patches of the flint gravel, which raise them out of the reach 
of the floods by which the lower fen-lands are occasionally submerged. ‘The out- 
crop of the lower greensand gives a swelling surface of dry land, so that its range 
through the marshes may sometimes be traced by a line of villages and steeples, In 
like manner the great outlier of lower greensand (the true Isle of Ely, which Wil- 
liam the Conqueror could only reach by an artificial causeway across the marsh of 
the Kimmeridge clay) is marked by the towers of Ely Cathedral and the steeples of 
Wilburton and Haddenham. With the exception of these elevations, all the country 
above described to the west of the chalk, is at a nearly dead level. Immediately 
under the vegetable soil are found silt of various kinds, remains of ancient forests, 
and bog-earth occasionally of considerable thickness. In some places the deposit is 
simple, in others complex, indicating many successive changes in the condition of 
drainage. Among these marsh lands are many traces of works by the hands of 
man. But the most interesting remains are those which occur at the base of the 
series, on the immediate surface of the older deposits, and they give an indication of 
the condition of the country before the turf-bogs dammed up the old water-courses, 
or the labours of man interfered with their distribution. Among these remains the 
author only notices such as are found in the Cambridge collection, and to the in- 
spection of which the Association was invited. Among these are the following :— 
