WATFOED JTATUEAL HISTOIIT SOCIETY. xli 



Field Meeting, Hth Jtjxe, 1S76, 

 BoxMOOR, Bennet's End, and Nash Mills. 



Meeting at Boxmoor station at about half -past two, the members, 

 under the guidance of their President, Mr. John Evans, went direct 

 to the Chaik-pit on Rough Down, where there is an exposure of 

 the band of hard, cream-coloured chalk known as the "chalk-rock," 

 which here forms the highest bed of the Lower Chalk, and divides 

 it distinctly from the overlying Upper Chalk or " chalk-with-tlints " 



This chalk- rock is well known, through the researches of Mr. 

 Evans, as the principal fossiliferous bed of the Chalk in this area. 

 It crops out near the highest part of the pit, which is a hollow cut 

 out of the hill-side. Its thickness is here about 18 inches, — the 

 upper portion, for three or four inches, consisting almost entirely of 

 nodules which contain about 10 per cent, of phosphate of lime. 



To get at this bed the steep face of the pit had to be scaled, and 

 the bed when reached was found to have so suifered from the re- 

 peated attacks of geologists, that, instead of projecting, as from its 

 hardness it would naturally have done, it was sunk back from the 

 face of the pit, rendering it no easy matter to work at it. A number 

 of fossils were however found,, including an Inoceramus, a Trochus, 

 a Rhynchonella, Terehratida cornea and semi-globosa, Ananchytesovatiis, 

 Spatangics cor-anguinum, and two species of Ventnculites. In 

 addition to these there have been found in the chalk-rock in this 

 pit, almost entirely by Mr. Evans, undetermined species of Bacu- 

 lites, Nautilus, Turrilites, Inoceramus (two species), Micr aster, 

 Parasmilia, Ocellaria, etc., and the following named species : — 



jiinmonitcs prosperianus. I Spondijlus spinnsus. 



Scaphites cequalis. Rhyiichonclla Mantelliana. 



Spondyhis latus. \ Terehratula biplicata. 



After botanising a little on Eough Down, the members, some 

 walking and others driving, proceeded to the Bennet's End brick- 

 field, noticing on the way the Boxmoor thistle, and other interesting 

 plants pointed out by Mr. Pry or, and a well-marked " pipe " near 

 Bennet's End, to which attention was directed by the President, 

 who explained its formation by the percolation through the Chalk 

 of water with carbonic acid in solution. At the brick-fields Mr. 

 Evans also gave an interesting account of the beds exposed, the 

 conditions of deposition of which, and the fossil contents, are 

 known chiefly through his researclies. These brick-fields are in an 

 outlier of the Lower Tertiaries, which are supposed to have been 

 saved from denudation, partly, by a slight change of dip in the un- 

 derlying Cbalk — a cause to which se-veral lines of similar outliers 

 in this and other Chalk districts are most probably due — but chiefly 

 by a fault in the Chalk, ruuiiiug north and south, against the face 

 of which the London Clay with its basement-bed, and the plastic 

 clay of the Woolwich and Reading Series, abut, and towards which 

 they dip at a slight angle. There are also other minor faults, 

 one of which throws the London Clay against its basement-bed, and 

 another the London Clay and underlying Beading Beds against a 



VOL. I. — PT. VII. P 



