188 
THE CRETACEOUS ROCKS OF BRITAIN. 
Firm greyish-white chalk ------ 
Tottern f ^ im 8 Te y sandy stone in thick beds 
I Hard brownish stone in two massive beds 
q. | Similar stone in three courses, with many phosphatic 
oue * f nodules at the base ------ 
Soft marl said to lie below. 
ft. 
5 
9 
8 
5 
The middle beds are those usually quarried, and they are traversed 
by wide vertical joints, into which the hand can be thrust, and by 
which the mass is broken up into large blocks weighing from two to 
three tons apiece. All the beds contain the characteristic bits of 
brown phosphate, but the upper beds are less hard, and Hake oh 
more easily under the action of weather and frost. The ‘upper 
surface of the stone is fairly well marked. 
Totternhoe Stone is exposed in the cutting on the Midland Railway 
near Charlton, and in a small quarry above the cutting on the 
eastern side. 
The next complete section through the stone-beds is in the large 
quarry at Arlesey, north of Hitchin and south-west of the County 
Lunatic Asylum. The section seen here in 1884 was as follows : — 
ft. 
Soil and chalk rubble - 3 
o Hard brownish-grey stone in thick beds, with many 
83 o3 fossils - - 10 
% Greyish marly chalk, includingn band of very soft marl 6 
^ ^ Very hard sandy stone, with green-coated nodules 
EH (phosphatic) as large as walnuts - - - 1-| 
Soft grey sandy chalk, passing into soft grey marl - - - 6j 
27 
The nodule bed at the base of the stone is a marked feature in 
this section, and is found again in Cambridgeshire. Subsequent 
excavations here (during 1886 and 1887) showed the base of the 
Totternhoe Beds for 110 yards inclined towards the north-west 
at about 7 °. The soft grey marl below was proved to be 20 feet 
thick at the south-east end of this section, and underlain by pale 
bluish marl, while at the north-west end only 7 feet of grey marl 
intervene between the Totternhoe Stone and the blue marl, the 
surface of the latter being nearly level. Hence there appears to 
have been erosion of the grey marl before the deposition of the 
Totternhoe Stone, resulting in the formation of a trough, which 
was filled up by the Totternhoe Beds. 
Chalk above the Totternhoe Stone. —The workable stone 
generally passes up into light grey chalk, of which there is usually 
about 35 or 40 feet; the grey passes into a nearly pure white chalk, 
the change often taking place in the space of 9 or 10 inches, and 
this white chalk has a different microscopical structure from the 
greyer chalk below (see p. 304). In Bedford and Herts the thick¬ 
ness of this white chalk does nut vary so much as it does in Bucks; 
it is usually from 20 to 25 feet thick, and there is often a passage 
at the top into the grey marly chalk of the overlying zone. 
