732 PROF. J. W. JUDD ON THE NATURE AND RELATIONS OF 
Jt is a well-known fact that the level at which the Chalk has been 
reached in different wells within the London Basin has varied 
within very wide limits. Thus at Meux’s Brewery the surface of 
the Chalk is only 71 ft. below O.D.; at Kentish Town it is 138 ft. 
and at Crossness 133 ft. below the same level. 
At most places in Surrey near Richmond, such as Wimbledon, 
Mortlake, Morden, and Wandsworth, the surface of the Chalk is 
about 250 ft. below O.D.; but at Kingston it is said to be 346 ft. 
and at Claremont 458 ft. below that level. 
As the thickness of the Chalk strata beneath London appears to be 
tolerably uniform, averaging about 650 ft., the irregularities in the 
surface of the formation must be due to the undulations into which 
the strata have been thrown. A fault or series of faults, very 
nearly coincident with the line of the Thames Valley, ranges east 
and west from Erith and Greenwich to Windsor, and there is 
evidence that, parallel with these, there exists a series of long folds 
accompanied in some cases probably by dislocations. These undula- 
tions of the strata are a resultof thatgreatsystem of movements which 
took place in Oligocene and Miocene times and were probably 
connected with the elevation of the Alpine chains. The effects of 
these movements upon the Chalk strata have been very carefully 
investigated by MM. Hébert and Barrois. Richmond appears to be 
situated on the downthrow side of the series of faults which traverse 
the London Basin from east to west. 
At a depth 924 ft. from the surface, the Richmond boring 
reached strata which, as we shall presently show, unquestionably 
represent the Upper Greensand. ‘Thus the whole thickness of the 
Chalk, including the white chalk, the grey chalk, and the chalk marl, 
is 671 ft. This thickness is slightly greater than that found in 
the more central parts of the London Basin. Thus at Kentish Town 
the Chalk is 645 ft. thick; at Meux’s Brewery 6553 ft.; at Crossness 
6374 ft. But on the other hand the thickness of the Chalk at Rich- 
mond is considerably less than at Turnford near Cheshunt in the 
northern half of the London Basin, where it was found to be no less 
than 730 ft. In passing still further northwards and eastwards 
we find that successively higher members of the Chalk have escaped 
the pre-Tertiary denudation, and thus the Chalk attains a thickness 
of 817 ft. at Coombs near Stowmarket, and of 1140 ft. at Norwich. 
Those who are familiar with the sparse distribution of the larger 
fossil organisms in the Chalk strata, will be prepared to learn that 
but few fossils were detected in the comparatively small cores brought 
up from this boring; such occasional fossils as were found proved 
quite insufficient for defining the several paleontological zones 
which are now known to be represented in that great formation. 
The microzoa, which are so abundant in the Chalk, have not, up to 
the present time, had their vertical distribution so carefully studied 
as to render us much aid towards the same end. It is a fortunate 
circumstance, therefore, that by the study of the series of cores from 
the Richmond boring it has been found possible to recognize two 
