BAGSHOT STRATA FROM ALDEBSHOT TO WOKIKGHAM. 493 



occurs next above it, appears to have been overlooked by the 

 Surveyors, though it crops out in many places. There is some indi- 

 cation of considerable contemporaneous erosion in some sections 

 where the pebble-bed rests upon this loamy bed ; and in the bed 

 itself thin seams of jpipe-claif generally occur. On this last point, it 

 would seem, my observations differ from those of the Surveyors *. 

 Grains of quartz coated with black and green amorphous matter of 

 vegetable origin are scattered freely in this bed : they are especially 

 numerous in juxtaposition with the pipe-clay layers. 



Detailed Sections. 



As these are rather numerous, and are spread over a rather large 

 area, extending about 13 miles from north to south, it will tend to 

 simplify matters if we consider these sections in two series : — a. Deep- 

 well sections, giving the whole range of the Bagshot Sands, and in 

 some cases the London Clay as well ; h. Sections in which only por- 

 tions of the Bagshot Sands are exposed. We shall find the general 

 character of the three divisions of the Bagshot strata sufficiently 

 determined by the evidence afforded by the former series to aid us 

 considerably in determining the stratigraphical horizons of the 

 sections of the latter series. 



a. Deep-Well Sectiois^s. 



(1) Well-section at Wellington College. — The specimens and 

 measurements of the strata pierced in digging this well were pre- 

 served with great care. The sectional diagram (fig. 1) has been 

 reprinted (with additional notes), Avith the courteous permission of the 

 President and Council of the Geologists' Association, from vol. vi. of 

 the ' Proceedings ' of that Society. The grouping of the strata agrees 

 substantially with that adopted by Prof. Prestwich many years agof. 

 A few supplementary notes, for which there is not sufficient space 

 on the margin of the diagram, may be useful. 



No. 2. This is a quartzose sand, stained with carbonaceous matter 

 on the grains, with scarcely a trace of iron. The occurrence of this 

 bed of dirty sand here is exceptional ; this horizon is generally 

 occupied by a bed of stiff yellow loam, almost a claj^, which passes 

 up into the yellow sands. 



No. 5. This bed was worked for about twenty years in the neigh- 

 bouring brick-field, and Wellington College was built with bricks 

 for which it afforded the sole material. 



* See Memoirs of the Geological Survey, vol. iv. pp. 329, 330, where the bed 

 is described as " a bed of ferruginous sand without pipe-clay." The general 

 outlines of Bagshot stratigraphy are given so fully in that work as to require no 

 further description here. It has been generally assumed, but, I think, never 

 proved, that this area of deposition was continuous with that of Hampshire 

 through Bagshot times. 



t Quart. Journ. Geol. Soc. vol. iii. loc. cit. As before intimated, however, 

 I draw the upper boundary of the Middle Bagshots at a rather higher horizon. 



