Vol. 50.] BORINGS AT CULFORD, WINKFIELD, WARE, AND CHESHUNT. 511 



Below the Gault hard dull-purple shale or rnudstone was found, 

 and similar material was penetrated for 29|- feet. This rock was 

 identified as Devonian by Mr. Etheridge, from its fossils. It is said 

 that the dip was ascertained to be about 30° S.E. A sample sent us 

 bv Mr. Francis has tool-marks on the outside, and if these are taken 

 to be horizontal the divisional planes show a dip of 40°. There are 

 specimens in the Museum of Practical Geology at Jermyn Street. 



From the data above given and those published in the ' Geology 

 of London ' we have constructed the following abstract of the beds 

 proved by this boring : — 



River Drift and Eocene Beds 



Chalk, with many layers of flints 



Chalk, described as ' chalk-rock ' 



Hard tough chalk 



Chalk, described as ' chalk -rock ' 



Chalk of varying hardness, some beds hard, some soft, 

 and some tough. This is probably all Middle 

 Chalk 



Chalk, described as hard and tough, with 7 feet of 

 mild chalk in the middle (? Lower Chalk) 



Hard whitish chalk 



Tough light-grey chalk 



Alternations of soft grey marl and hard chalk 



Firm, grey, silty chalk and chalk-marl, with two beds 

 of hard grey chalk 



Chalk Marl, passing down into Chloritic Marl 



Upper Greensand. Fine greenish sands, with beds 

 of hard calcareous sandstone at intervals, the 

 lastat 825 feet 



Gault. Silty calcareous clays in the upper 20 feet, 

 then compact grey clays, with a bed of greensand 

 and phosphate-nodules at the base 



Devonian. Hard dull-purple mudstones 



Thickness. 

 Feet. 



260* 



15 



46 



6 



170 



44 



153£ 



29* 



Depth. 

 Feet. 

 102J 

 363 

 378 

 424 

 430 



600 



25 



625 



35 



660 



73 



733 



29 



762 



17 



779 



4 



783 



827 



980i 

 1010 



VI. Conclusions. 



Amongst points of general interest is the fact that the floor of 

 older rocks has now been struck at a much less depth than before. 

 Ware held the first place with a depth of 79G| feet, but now Culford 

 takes it with only 637|, or 159 less, measuring from the surface. 



For the proper consideration of the subject, however, it is needful 

 to refer the depth of the various borings to one level instead of 

 reckoning from the surface, in which latter case the height of the 

 ground affects the result. This height is, of course, a varying factor 

 which has nothing to do with the position of the older rocks, being 

 due to actions that have taken place in late geologic time, to erosive 

 work of a purely superficial kind, affecting the thickness of the 

 Tertiary beds and sometimes of the Chalk, but disconnected from 

 all other beds beneath. The depth from the surface, depending as 

 it does on the level of the ground, is a matter of no moment, 

 except locally. 



