On Artesian Wells near Silsoe in Bedfordshire. 103 



almost as readily as the " Bath stones " employed for household 

 purposes. 



In the accompanying section — between Silsoe (1) and the hills 

 above Barton-in-the-Clay (2) — A represents the lower greensand, 

 B the impermeable calcareo-argillaceous strata (gault, upper 

 greensand, chalk marl), and C the middle chalk. Layers of drift 

 coat these more or less ; ^.^ — 



and on some of the in- "^ -2 X 



tervening heights, as at i ' y ^ 



Higham Gobion, &c., — "^T"^ . - . - — -^^ ■ 



the top of the hill is j^ , -B 



capped by a thick mass 



of chalk-like detritus mixed with rolled pebbles and a few fossils 

 of the gault and other strata, underlying two or three feet of 

 more modern alluvium or vegetable mould. The fossil speci- 

 mens consist principally of belemuites [B. minimxis, &c.), and of 

 two or three species of Ostrese. All of these are much roUed and 

 water-worn, the Ostrese pi'esenting only single valves, and some 

 of the larger belemnite guards being spUt longitudinally so as 

 to show the phragmocone receptacle. 



In other parts of the district, the di-ift-gravel contains pebbles 

 of different kinds of granite, granular quartz, clay- slate, sand- 

 stone, iron-sandstone, flint, and iron pyrites converted into the 

 hydrated sesquioxide of iron. The latter bodies are evidently 

 derived from the chalk, similar nodules, or rust-stained cavities 

 left by their entire decomposition, being seen in all the pits along 

 the chalk range. 



The lower greensand strata consist of soft and coarse sand- 

 stone beds, interstratified with bands of iron-sandstone and a 

 few subordinate layers of clay. A section is exhibited in the 

 quarry a little to the west of Silsoe Church. The beds — apart 

 from their false stratification, of which peculiarity they offer an 

 interesting example — are there seen to dip towards the south, 

 thus constituting a large natural reservoir lying beneath the 

 impermeable strata of the valley ; and as the chalk-marl and 

 gault series conjointly do not average more than 200 feet in 

 actual depth, a surface supply of water is readily obtainable. 



Tlie beds of the valley ai-e perfectly impermeable, and except 

 where the patches of gault clay occur, they are of a chalk-like 

 aspect. In this valley, within an area of about ten square miles, 

 from one to two hundred borings have been executed ; and in a 

 great number of instances the bore-holes produce an overflowing 

 stream. As a mean, it may be said that the water in a four-inch 

 pipe rises about four or five feet above the ground ; but this, of 

 course, varies with the surface-configuration of the valley. In 

 the higher parts, the water stands at a few feet below the surface, 



