THE JURASSIC DEPOSITS WHICH UNDERLIE LONDON. 7TA9 
as ink.” Itis not impossible, therefore, that actual Jurassic coal 
seams were passed through at this point. 
From a careful comparison of all the facts of the case, it is clear 
that while the Great-Oolite beds under the Tottenham Court Road 
were deposited in comparatively shallow water, and in close proxi- 
mity to the land, the beds of the same age under Richmond were 
jaid down in much deeper water. Hence we may fairly infer that 
during the Great-Oolite period the northern half of the Paleozoic 
ridge under London formed dry land, while the southern half was 
submerged beneath the waters of the ocean, and became gradually 
buried under its sediments. 
XI. Tas Porxiiric (?) Strata. 
At 1239 ft. from the surface the boring at Richmond passed 
suddenly from the limestones and clays of the Great Oolite into red 
and variegated sandstones and clays (‘‘ marls ’’). 
The sandstones vary in colour through different shades of red to 
white and greenish tints. They are sometimes excessively fine- 
grained and very perfectly laminated, having the surfaces of the 
Jaminee covered with flakes of silvery white mica. At other times 
the sandstones are much coarser, so coarse indeed as almost to merit 
the name of grits, and their bedding is obscure. Clay-galls are 
found in some of the beds as well as impressions which may pos- 
sibly indicate the former presence of plant-remains that have now 
been entirely removed. The sandstones are sometimes traversed 
by thin veins of calcic carbonate. Particles of galena were found 
in these sandstones at a depth of 1293 ft. 6 in. 
The clays (“‘ marls ”) which alternate with these sandstones are 
of a dark red colour, mottled with green in blotches and spots. 
When brought up in solid lumps these clays are seen to be highly 
indurated and traversed by joints in various directions, the joints 
being coated with a green calcareous deposit. 
In some portions of these strata the marls and sandstones alter- 
nate in thin layers; in other portions we have a considerable thick- 
ness of marls; while sometimes the sandstones constitute tolerably 
thick beds. 
The following is the succession down to the lowest point 
reached :— ie Tht 
1. Alternations of red sandstone and variegated “‘ marls” ......... 16 0 
Pam blerede bed tOlesanGStONeHN. 2) eise sd vite bake ote tee eet eS ae 1 30) 
3. Marls with occasional beds of sandstone ..................eeceeeees 10 O 
4. Alternations of sandstone and “ marls” ..........2..2...eeecseeeeeees PAL (0) 
OME SOMCMSATLGSLOMEEGOC Kar. Sates ais eae elec omias ease hen eeemaem as ie 4 0 
OMMEGCOM ITA TIS terete mnceein a eke Moy 8 CWE 8 BL te Oe eee eee 2 6 
feeitard icamastoie anes ais chee. So Meee rph ae Le See AR 4 6 
8. Soft sandstone with many seams of “marl” ................:0:0000 5 0 
9. Hard red and white sandstone rock, coarse and gritty in some 
seams, with some bands of clay ...... s aigine'y deeasiusiezls tutte cisnedsr 17 O 
10. Beds of sandstone and red “ marls,” the latter predominating 
and causing much trouble by falling in and impeding the 
boring operationstyyy. Voice se steader ees headnad tat anc deena es 0 
(Owing to the difficulty of penetrating these rocks with the rope-boring 
machinery, in consequence of the falling in of the “ marls,” recourse was had to 
the diamond rock-drill.) 
