278 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 19, 



[Plates XVII. to XX.] 



§ 1 . The following observations are the result of a visit made in the 

 summer of last year (1851) to parts of French Flanders and Belgium, 

 undertaken with a view of comparing the tertiary strata of that part 

 of the continent with those of England. 



I shall first describe what I saw of the newest deposits, and then 

 proceed to consider the others in a descending series until I arrive at 

 strata which repose immediately on the chalk of Maestricht. 



For convenience of reference, and in explanation of the nomencla- 

 ture adopted, a synoptical table of formations (Table I.) is annexed. 



§ 2. Loess or Lehm (A. Table I.). Limon de Heshaye of 

 M. Dumont. 



The southern half of Belgium is overspread almost everywhere by 

 a continuous deposit of clayey loam, resembling in colour and com- 

 position the well-known "loess " of the Rhine. This loam has been 

 called "Hesbayan mud" by M. Dumont, because it abounds in the 

 ancient province of Heshaye, which includes, among other areas, the 

 country between Liege and Waremme and between Liege and 

 Tongres. It presents generally the same uniformity of aspect and 

 composition, and the same absence of stratification which characterize 

 it on the Rhine between Cologne and Basle. In Belgium, however, 

 land and freshwater shells are much more rare, and the only spot 

 where I met with any was at the village of Neerepen, between Tongres 

 and Hasselt (see Map, PI. XVII. fig. 4), where they had been pre- 

 viously remarked by M. Bosquet. Here I found abundantly the 

 Succinea ohlonga, so common in the Rhenish loess, and Helix hispida. 

 The tusks of a fossil Elephant were also obtained here by M. Bosquet. 

 The only shells which I heard of as having been detected elsewhere 

 in the Belgian loess consisted of recent species, all of terrestrial or 

 fluviatile genera. 



The thickness of the " Hesbayan mud " is variable, usually ranging 

 from 10 to 30 feet. It is seen capping some of the highest hills or 

 table-lands near Brussels ; as for example, that above the villages of 

 Jette and Dileghem, west of Laeken (see Map, PL XVII. fig. 3), at 

 the height of about 300 feet above the sea. At the base of the 

 loess, or between it and the older rocks, there occur very generally 

 one or more beds of gravel. In some cases, as I shall hereafter have 

 to point out, where it rests on unconsolidated tertiary sands and 

 loams, there is such an intermixture of the newer and older deposits, 

 owing to denudation and redeposition (the fossils washed out of the 

 older beds often remaining entire), that it is most difficult to draw a 

 line of separation. 



The homogeneous character of the loess throughout the hydro- 

 graphical basin of the Rhine always disposed me to refer its origin to 

 some common source, such as a great river which had brought down 

 for ages the same kind of sediment, and spread it over a large area, 

 while that area was slowly subsiding. I also supposed that the same 

 region had been subsequently re-elevated and denuded, so that most 



