70 Dr. Aubrey Slrahan — Geology at the Seat of War. 



chalk escarpments of the North and South Dowus are continued in 

 the chalk escarpments which overlook Boulogne is obvious, and that 

 the subdivisions of the Tertiary strata with which we are familiar 

 in the London and Hampshire Basins are recognizable in the North of 

 France and in Belgium is well known. Not only so, but the scenery 

 characteristic of each formation is reproduced with fidelity. 



In one respect only the Continental deposits differ materially from 

 those of our home counties. Over wide tracts there has been 

 distributed, up hill and down dale, a fine yellow loam, the Union of 

 Belgian geologists, which is doubtfully, if at all, recognizable in 

 England. The thickness varies from 100 feet in the valleys to 

 a mere trace on the flanks of the higher hills, where it shades into 

 hili-talus, but the material is generally spread as a mantle over the 

 country regardless of elevation. This is the deposit with which our 

 men are generally in contact in trenches and the smaller dug-outs, 

 and which is in evidence on the clothes of those returning from the 

 Front. 



Much has been written on the origin of the Union. It has not the 

 character of a stratified subaqueous deposit, and its fossils include no 

 marine and but few freshwater shells. Land shells, however, are 

 embedded in it, with the bones of various herbivorous and carnivorous 

 mammals. Judged by all these characters, its uniformity of grain, its 

 disregard of level, and its fossil contents, it has been attributed in the 

 main to subaerial agencies. It is in fact a dust, distributed by the 

 wind and retained wherever it settles on ground thickly clothed with 

 vegetation. Like the loess, with which it has many characters in 

 common, it appears to have been formed in countries which suffer 

 from extreme alternations of dry and wet seasons. 



In dry weather the Union readily returns to a condition of dust ; in 

 wet weather it forms a mud unlimited in quantity and obstructiveness. 

 But as a material in which trenches and dug-outs can be excavated 

 with the minimum of labour it seems to have found some use. Under 

 the Union and for the most part visible only by means of wells or 

 boreholes, lie the Tertiary and Cretaceous formations. 



The southern margin of the Tertiary tract, which includes the 

 London and the Belgian Basins, runs near Basingstoke, Guildford, and 

 Canterbury to the coast near Deal. It strikes the French coast south 

 of Calais, and passes thence by Bethune, Mons, Namur, and Liege. 

 As far as Bethune the margin lies within the lines of the Allies as at 

 present situated, but thence southwards it passes into ground occupied 

 by the enemy. 



Along parts of the margin the strata, both the Tertiary beds and 

 the Chalk below them, are tilted up at a high angle, as for example 

 near Guildford, and in such a case the Chalk projects in a ridge, 

 typically illustrated in the Hogs Back. But on the Continent the 

 Chalk emerges at a gentle angle, and the passage from rolling Chalk 

 downs to low undulating plains of Tertiary beds is gradual. Indeed, 

 outlying patches of Tertiary beds, from a few acres to a few square 

 miles in area, are scattered abundantly over the higher parts of the 

 downs. Geologically this tract is comparable to many parts of 

 Hertfordshire, Buckinghamshire, Berkshire, Surrey, and Kent, and 



