Fisher—Natural Pit at Lexden. 101 
series and the lowest Silurian rock is a good reason for believing 
that the gneiss of Bohemia and Bavaria is truly the represen- 
tative of the Laurentian or Fundamental Gneiss.* 
II.—On a Suppen SINKING oF THE SoiL IN A FIELD AT 
LEXxDEN IN ESSEX. 
By the Rey. O. Fisuzr, M.A., F.G.S. 
a the month of May, 1861, there occurred a curious subsidence of 
the soil in a field on the ‘Malting Farm’ at Lexden in Essex. 
The cavity thus produced was about twenty-five yards in circum- 
ference, of an elliptical form, and about twenty feet in depth, with 
the sides slightly overhanging. The subsidence took place quite 
suddenly; some workmen, who were in the field in the forenoon, 
finding the pit fresh formed on their return from dinner. The ground 
in which the pit is situated consists of a slightly rising bank of 
valley-gravel, and is about fifty yards to the south of the little River 
Colne, which runs past the spot, and gives its name to the ancient 
town of Colchester. The surface of the field cannot be more than 
five or six feet above the stream when full. 
The sides of the pit are clean-cut in the gravel, which is stratified 
and has evidently never been disturbed. Though at the time of the 
occurrence the event excited great local interest, yet I did not 
myself hear of it until a year ago. I then found it, after a rainy 
time, containing a little water at the bottom, in the funnel-shaped 
cavity which was formed of the impervious surface-soil that had 
subsided ; but it was evidently not spring-water. See the accom- 
panying section. 
River Colne, <—_______50 yards. _—_____> 
Diagram-section of a Natural Pit near Lexden, Essex. 
a. River-level. b. Low-level Gravel (6 feet thick above the river-leyvel). 
Such are the phenomena: and the question is, how are they to be 
explained ? The subsoil of the valley is London Clay, which is seen 
at the bottom of Lexden brick-pit (that cemetery for extinct 
Pachyderms; see Quart. Journ. Geol. Soc., vol. xix. p. 393), about half 
* Quart. Journ. Geol. Soe., vol. xix. p. 359. Looking to the total divergence of 
their strike, I am of opinion, that the Laurentian rocks of the North-western High- 
lands, as well as those of the North-west of Ireland, will prove to be the ‘Lower 
Laurentian’ of Logan. 
9 
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