THE JURASSIC DEPOSITS WHICH UNDERLIE LONDON. 751 
[That the strata met with in the deepest portion of the Richmond 
well resemble, in the most striking manner, the rocks of both the 
Old and the New Red Sandstones, every one who has examined them 
must be convinced. Some of the beds, it is true, appear to be of a 
somewhat more compact and indurated texture than is usual in the 
rocks of those formations when exposed at the surface; but this is 
no more than might be anticipated when we bear in mind the great 
thickness of superincumbent strata which has had to be pierced 
before reaching them. 
Unfortunately the strata of the Old and the New Red Sandstones, 
in the absence of all fossil evidence, do not present any character- 
istic differences which we can rely upon as a means of discrimi- 
nating the deposits of pre-Carboniferous age from those which are 
post-Carboniferous. Under these circumstances we are compelled 
to rely upon other considerations than those of general resemblance 
in trying to arrive at a judgment concerning the age of the red 
rocks at Richmond. 
The possibly high angle of dip of these strata (though it must be 
remembered that this has not been certainly proved) may appear, at 
first sight, to afford an argument in favour of the Paleozoic age of 
the rocks in question; but when we remember the great stratigra- 
phical break which undoubtedly exists at the base of the Great 
Oolite, it would not be surprising to find that strata of Permian or 
Triassic age had been greatly disturbed before the deposition upon 
them of the Bathonian beds. On the other hand, the presence of 
disseminated particles of galena, and the considerable proportion of 
chloride of sodium in the water obtained from these red rocks at 
Richmond, are obvious points of analogy with the Triassic strata. 
In a subsequent part of this paper I have dwelt at length upon 
those general considerations which appear to me strongly opposed to 
the view that the Richmond beds are of Old-Red-Sandstone age, 
and which lead me to the conclusion that the balance of evidence is 
in favour of their being regarded as the New Red Sandstone, and 
therefore of post-Carboniferous age. | 
As it would, I think, be hazardous to offer a suggestion with 
respect to the particular portion of the series between the Carboni- 
ferous and the Lias with which the red and variegated beds under 
Richmond should be correlated, I have ventured to call them doubt- 
fully ‘‘ Poikilitic.” 
Subsequently to the reading of the first part of this paper before 
the Society two discussions on the nature of the rocks found in the 
Richmond well took place in the Geological Society of the North 
of France, at Lille. In the first of these discussions the speakers 
were inclined to entertain the possibility of the variegated beds in 
question belonging to the Gédinnien (Lower Devonian). 
At the request of M. C. Barrois, I sent a series of specimens of 
the different varieties of rock met with at Richmond, and in a 
second discussion M. Gosselet, M. Achille Six, and M. C. Barrois all 
maintained the view that these beds could not be referred to any 
part of the Devonian series, but really belong to the Trias *. 
* Annales Soc. Géol. du Nord, vol. xi. p. 144. 
