221 
Dr Fleming on the Geological Deluge. 
Mr Greenough, a strenuous supporter of the diluvian hypothe- 
sis, has stated in his Geology (p. 121.), that 44 the valley of the 
Thames, in London, is contained in that of which Clapham Rise 
forms part of the boundary on one side, and the Green Park on 
the other ; and this,, again, is contained in the larger valley, 
which occupies the interval between Highgate and Sydenham. 
Arrived at these points, we find our horizon bounded by a chalk 
ridge still loftier.” These included valleys throw great light on 
the history of the globe. They are like the circular valleys in 
river courses : they mark some of the features of a former state 
of things ; they assist us in tracing the changes which have taken 
place, and even the agents concerned in their production : but 
they give us no dates. 
11. Formation of Gravel Beds .— The materials of which these 
beds consist, appear, in general, to be rounded blocks of rocks, 
confusedly mixed together, or presenting but indistinct marks of 
stratification. The blocks are seldom angular, and never exhibit 
the surfaces or edges of a mass recently detached from an un- 
disintegrated rock. As these masses are supposed to have been 
derived from the rocks which the geological deluge tore from 
their beds during the excavation of the valleys, we might expect 
to find them exhibiting numerous instances of tolerably fresh- 
least, two of the 44 modern strata.” Nor was I disappointed ; for that which 
my opponent has pronounced diluvium, I found to be Lacustrine Silt ; and 
my conclusion rested on the following facts : 1. The beds, and their stra- 
ta of fine clay and sand, are nearly horizontal. 2. They contain, here and 
there, thin horizontal patches of small rounded flinty pebbles, (precisely simi- 
lar to small layers of gravel which I had seen in genuine examples of similar 
origin), indicating the influence of occasional floods. 3. Scattered through the 
clay, I observed several pieces of shells, the present inhabitants of our lakes 
or slow running streams, viz. Helix peregra and complanata , Turbo fontinalis , 
and Cardium corneum of Montagu. It is evident, therefore, that a lake existed 
here which has been filled up by slow degrees, and the character of the mate- 
rials, and organic remains of the different beds, mark certain epochs in the 
process. It is fortunate that this example occurs so near London as to be of 
easy access to the members of the Geological Society. Perhaps a good deal 
of the] reputed English diluvium may, upon investigation, be found to be la- 
custrine silt, as in the present instance. 
. VOL. XIV. NO. 28. APRIL 1826. 
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