72 Dr. Aubrey Strahan — Geology at the Seat of War. 



The Paniselien and Bruxellien Sands absorb a large proportion of tbe 

 rain that falls upon them, and give out the water as springs at their 

 base, where they rest upon impervious clays or along any interbedded 

 clay-hand. Bailleul draws, or used to draw, a part of its supply 

 from a spring of this character in the side of Mount Noir, one of the 

 hills south of Ypres. Ypres was supplied by similar springs at 

 Dickebusch and Zillebeek, but the gathering-ground of the springs 

 includes the scene of some of the most murderous fighting of the 

 war, and it may well be questioned whether water drawn from sucli 

 an area can be usable. In other parts of Belgium a system, which is 

 rarely seen in Britain, of driving tunnels under the larger tracts of 

 such sands and collecting the water by branching galleries, has been 

 adopted. Brussels is partly supplied in this way. 



The Chalk of the South-East of England includes three subdivisions 

 of more or less distinctive lithological characters. The Upper Chalk 

 is a massive type of chalk set with nodules or rows of nodules of 

 flint. This subdivision ranges to upwards of 600 feet in thickness 

 and forms the upper and bolder part of the chalk escarpments. The 

 Middle Chalk is a thick-bedded chalk generally devoid of flints, and 

 the Lower Chalk includes much chalk marl. The Upper Chalk is 

 the source of water of the majority of chalk wells. The Lower 

 Chalk, on the other hand, though it may hold much water, yields it 

 but slowly on account of its marly and almost impervious character. 

 For this reason the Lower Chalk has been much discussed as a suitable 

 stratum in whicli to drive a tunnel from Dover to Calais. In fact, 

 the small part of the tunnel which has been driven is situated in this 

 subdivision. 



In the North of France these subdivisions of the Chalk present 

 much the same characters as in the So\ith-East of England, but there 

 extends from near Calais towards Mons an underground bar, which 

 clearly existed in the Cretaceous sea as a ridge or at any rate an 

 obstruction to the free circulation of currents. The Upper Chalk, 

 though it crosses the bar, changes its character. The whole formation 

 assumes a marly character under Flanders, and loses its value as 

 a reliable source of good water. Herein lies the difficulty of finding 

 water supplies in Eastern and Western Flanders. The Landenien 

 water is often not potable, and the Chalk yields none. The Palaeozoic 

 rocks beneath yield salt water, if any, and the uplands of Paniselien 

 Sand are too limited in area to give a sufficient supply by gallery. 

 Under these circumstances recourse has been had to rain and canal 

 water, rendered harmless, as believed, by chemical treatment and 

 filtration. So keenly was the lack of good water felt that a project 

 was on foot before the War to supply the towns of Low Belgium from 

 a source in the Ardennes. The supply had been carried to Brussels, 

 and its further distribution was in progress when the War broke out. 



Chalk forms one of the most suitable rocks for dug-outs, provided 

 that the excavations are not carried below the level of the under- 

 ground water. It is not difficult to excavate, and yet firm enough to 

 stand fairly well. The extensive and elaborate system of under- 

 ground dwellings recently captured by our troops have been 

 excavated in the Chalk. 



