200 H. M. Jenkins — Surface-Geology of Belgium. 



of from 20 to 25 feet per mile, instead of one of 3 inclies ; (2.) The 

 parallelism of the lines of 75 and 150 feet elevation ; and (3.) The 

 parallelism of these liaes with the line of junction of the Campine 

 sands and the Limon de Hesbaye. 



South-east of the 150 foot contour-line the inclination of the surface 

 again becomes comparatively gradual, though somewhat irregular 

 and more interrupted than was the case in the sandy zone ; but from 

 the 150 foot line to the valley of the Meuse, a distance of about 60 

 miles, the rise is not more than about 350 feet, the north bank of the 

 river having an average height of about 500 feet above the sea level. 

 This rise indicates a gradient of less than six feet per mile, or not 

 much more than one-fourth of that just noticed — a fact sufficiently 

 remarkable when placed in contrast with the former abrupt declivity, 

 and with what is seen on the south bank of the river valley. 



The line of 600 feet elevation runs about two or three miles to 

 the south of the Meuse valley, and is succeeded southwards, at a 

 mean distance of about four miles, by the line of 800 feet elevation, 

 the gradient between these two lines being, therefore, as high as 50 

 feet per mile. The succeeding flatness, as already described in the 

 previous cases, is once more seen south of the 800 feet line, for it 

 requires a journey of about 20 miles (except in the extreme easb of 

 the Ardennes) to reach the line of 1,000 feet elevation, thus showing 

 that the gradient has fallen to about 10 feet per mile. South of this 

 " inclined plane " we meet with another and still more abrupt 

 gradient, and then reach the broken plain and the isolated eminences 

 of the Higher Ardennes. 



The significance of these facts to the geologist and the physical 

 geographer appears to me so obvious that I shall mention but very 

 briefly the conclusions which they forced upon my mind. In the 

 first place, the Limon de Hesbaye rarely crosses the gorge which 

 forms the Meuse valley. I have, therefore, for agricultural purposes, 

 mapped all the tract of country south of the Meuse as " Strong 

 Plateau-land ;" but geologists know very well that the Condroz and 

 the Ardennes, which comprise that tract, consist of certain Pala30zoic 

 rocks, overlain in places by patches of drift (Cailloux Ardennais) 

 near the numerous watercourses. This drift, containing rocks of 

 Ardennes origin, is also found beneath the loam in the Hesbaye and 

 beneath the sand in the Campine. 



North of the Meuse, and at a lower level, therefore, is the more or 

 less broken plateau, having the Limon de Hesbaye as its surface- 

 deposit ; and north of this loam, at a still lower level, is the plateau 

 composed of the Campine Sands. This terrace arrangement, in 

 reference to the geological age of the surface-deposits of Belgium, 

 seems to me capable of but one interpretation — namely, that the 

 Ardennes drift ( Cailloux Ardennais) is the oldest of the deposits, the 

 Limon de Hesbaye the next in succession, and the Campine Sands 

 the youngest of all, with the exception of the Polders, which we 

 know to have a historic date. 



The Campine Sands were regarded as contemporaneous with the 

 Limon de Hesbaye by M. Dumont, and as older than it by M. 



