J 8 
T. E. L0NES—FOSSILIFEROUS 
and sand consist mainly of coarse and sharp sand, unworn flints, 
and flint-pebbles, and contain numerous white quartz-pebbles, a 
few quartzite-pebbles, and some irregular masses of peat. A small 
piece of bone, a splinter probably from a leg-bone, was found by 
me in one of these masses of peat, but the bone was too small for 
determination of the species of animal to which it belonged. The 
following is a list of Mollusca found in the light-coloured clay, 
the species having been determined by Mr. E. T. Newton, E.R.S., 
of the Geological Survey: —Helix arbustorum. If. caperata, If. 
nemoralis , Bithynia tentaculata , Pisidium amnicum , Limncea perceger , 
L. palustris, Succinea putris, Planorbis carinatus, P. vortex. 
Fig. 19.,— Section at the Gas Works, Watford. 
Having described the beds themselves, we may next enquire 
how far they enable us to theorize on the physical conditions of 
the Colne Yalley at the periods during which they were deposited. 
For this purpose, the most interesting are the fossiliferous beds 
marked 4 and 5 in the section. It is generally admitted that 
at a period very recent, geologically speaking, but very ancient 
from an ordinary point of view, the climate of this country w r as 
very much colder than it is now, and that most, if not all, 
parts of England north of the Thames Yalley were covered by ice 
and snow. During this period extensive deposits of clay, gravel, 
and sand, containing materials transported from a distance, were 
laid down beneath or near the icy coverings. These and other 
deposits formed by various agencies during this cold or glacial period 
are commonly known as glacial deposits or drift. 
