session 1904-1905. 
Ixi 
geographical objects. They should he recorded and sent to the 
Secretary of the British Association. 
The Rev. T. R. R. Stebbing (Section D) said that a Committee 
of his Section suggested for investigation the following subjects:— 
(1) Cave faunas; (2) zoological changes on a given plot of land 
(luring the year; (3) compilation of local faunas ; (4) systematic 
observations on the micro-organisms of a given pond or ditch ; 
(5) overland lines of migration of birds; and (6) collection of 
slugs from all parts of the British Isles. 
Field Meeting, 8th Apeil, 1905. 
WELWYN AND DATCHWOETH. 
This was a joint meeting with the Geologists’ Association, under 
the direction of Dr. A. E. Salter for that Association and of 
Mr. Hopkinson for the County Society. 
On arrival at Welwyn Station at about 3 o’clock the members of 
the two societies walked to Datchworth by way of Harmer Green 
and Woolmer Green, which are situated on a Tertiary outlier owing 
its preservation to a capping of gravel, and it was the object of 
this meeting to examine this gravel in various pits. 
The heterogeneous assortment of materials composing an ordinary 
gravel offers hut small attractions to the general observer, hut 
a geological student cannot rest satisfied until he has found a 
satisfactory explanation of the way in which the various constituents 
have been brought together and deposited in their present position, 
and no branch of geological enquiry has resulted in a greater 
difference of opinion and more lively controversy than the origin of 
our gravels. 
A section of gravel in Mr. Powell’s pit was first examined. It is 
stratified, varies from five to ten feet in thickness, and has false- 
bedded sand below it in one part of the pit. It is composed of 
Tertiary flint-pebbles, subangular flints, Hertfordshire conglomerate, 
dark chert, rough quartz blocks ranging up to four inches in length, 
light-coloured quartzites, handed rhyolite, jasper, grits, etc., the 
non-local material being chiefly Palaeozoic, while Jurassic fragments, 
Bunter pebbles, basalt, and granite appear to he absent. 
Dr. Salter’s conclusions are that these and all other similar 
gravels in Hertfordshire were formed and deposited in exactly 
the same way as similar gravel is being formed and deposited 
to-day by the constant dissolution of chalk and other soluble 
matter by rain-water, leaving insoluble stony fragments which 
have been gradually washed away, carried by rivers often for 
long distances, and finally deposited by slow degrees in favourable 
situations. He pointed out on this occasion that the gravel 
occupies a rather high position in the “Drift Series” connected 
with the Stevenage gap, and stated that southern Hertfordshire and 
