MAPS AS GEOGRAPHICAL ILLUSTRATIONS SOI 
and escarpment of the Ile de France, and the inner black-soil 
prairies of the cotton belt representing the lowland of the 
Champagne. The longitudinal arrangement of relief is in these 
cases entirely due to the occurrence of a more resistant stratum 
overlying a less resistant stratum. On sucha structure, the normal 
succession of features developed in the mature stage of dissec- 
tion—especially in the mature stage of one cycle following the 
old age of a previous cycle—is the znner lowland, where the 
weaker strata are worn down to faint relief; the zuface, where the 
retreating margin of the overlying group of harder strata now 
stands; and the outlooking slope, bevelling down the back of these 
harder strata to the next group of weaker beds, or to the coast. 
No name is yet suggested for the longitudinal upland that 
embraces both the steep infacing and the gentle outlooking 
slopes. The term “ridge” has been used, as in Clark’s account 
of the Cretaceous formations of New Jersey, but ridge is rather 
too emphatic for so broad and gentle an elevation as the 
uplands of this kind often present; and, moreover, ridge is a 
term of general application. What is needed is a term that shall 
be associated with the upland formed by a resistant stratum of 
gentle dip as distinctly as inface is coming to be associated with 
the inland facing escarpment of the upland. 
The district between the two master rivers, the Marne and 
the Seine, is very instructive in exhibiting a number of beheaded 
and diverted streams, such as are generally characteristic of the 
inner lowland of coastal plains having longitudinal features. No 
more perfect and symmetrical example of the kind has come to 
my notice. It may be explained as follows : 
At a much earlier stage of topographical development than 
the present, and before the weak calcareous belt was excavated 
to a significantly lower level than the harder arenaceous belt, 
three other streams ran westward between the Marne and the 
Aube-Seine. These streams may be called the Surmelin, Petit 
Morin, and Grand Morin, after the names of their present lower 
courses. The middle of the three forked into two branches, 
the Somme and the Vaure, just east of the line between the cal- 
