THE JURASSIC DEPOSITS WHICH UNDERLIE LONDON. — ae 
ft., at Scarle in Lincolnshire, at a depth of 1900, at Harwich at 
1025, and at Calais at a depth of 1032 ft. 
At Kentish Town and at Crossness strata of a somewhat anomalous 
and doubtful character were met with at depths of 1114 and 1008 
ft. respectively. 
Now at Burford, Poikilitic strata appear to have been passed 
through and to have had a thickness of 428 ft. At the St. Clement’s 
well at Oxford there is reason to believe, as shown by Professor 
Prestwich*, that Keuper beds were reached. At Gayton, about 
5 miles §.W. of Northampton, Poikilitic strata with a thickness of 
63 ft. were penetrated; while at Northampton strata, probably of 
the same age, but of very curious and anomalous character, were 
found lying between the Lower Lias and the Carboniferous rocks. 
These consisted of curious abnormal sandstones and conglomerates, 
often of a red colour, with some magnesian limestones, the whole 
having a thickness of 673 ft. There is a great probability that 
these strata are all anomalous representatives of the Poikilitic series, 
and they agree in position and thickness with the normal Trias beds 
found at three localities near Northampton, which is only five miles 
distant from Gayton‘. 
The materials brought up in the boring at Crossness, near Erith, 
were so broken and mixed up, owing to the method of boring employed, 
that the utmost that can be said concerning them is that they resemble 
the sandstones and “ marls” of both the Old Red Sandstone and of 
the New Red Sandstone series. 
The rocks met with at Kentish Town have, ever since their first 
discovery, proved a puzzle to geologists. They are certainly far less 
like the typical Poikilitic strata than those met with at Richmond. 
On the other hand they present some resemblances in their characters 
to the curious and anomalous beds found overlying the Carboniferous 
strata at Northampton. 
In recent years Professor Prestwich has felt constrained to 
abandon his former reference of the Kentish Town beds to the New 
Red, and has insisted on their resemblance to the Old Red of the 
Mendip Hills. Mr. Whitaker suggests an argument against the 
latter correlation, which I think is entitled to much weight. ‘ There 
is a strong reason against the classification of the bottom beds at 
Kentish Town and Crossness with the Old Red Sandstone, which 
seems to have escaped notice. Having the series unmistakably 
present in the Devonian type at Cheshunt and at Meux’s, it would 
be strange indeed were it to occur in its wholly distinct Old Red 
type at Kentish Town, between these two places, and at Crossness 
not very many miles from the latter of them! I believe that no 
such thing is known to occur anywhere, the two types of what is 
generally taken to be one great geological system being limited to 
separate districts, and not occurring together ” £. 
* Proc. Ashmol. Soc. 1876. 
+ [Since this paper was read, Mr. Kunson has given a very careful description 
of these interesting borings: see Quart. Journ. Geol. Soc. vol. xl. 1884, p. 482. ] 
{ Guide to the Geology of London, third edition (1880), p. 21. 
ee 
