502 SL(IDIIES, STOUR SIMCLOIGIN TOS 
careous and arenaceous belts. Since then, all the streams have 
deepened their valleys. The master rivers have cut down to 
the greatest depth. The three intermediate streams have cut 
down to a less depth. From all these deepening valleys subse- 
quent side-streams have grown out, roughly following the strike 
of the weak calcareous belt; but the most active and important 
of these belong to the two master rivers. Let us then consider 
particularly two of these subsequents ; one growing southward 
from the Marne, the other northward from the Aube-Seine. 
These master subsequents long ago beheaded the Surmelin and 
the Grand Morin, diverting their upper courses, the Soude and 
the Maurienne, to the appropriate master rivers, and leaving the 
upper part of their beheaded lower courses in shallow valleys on 
the sandy upland. The escarpment has probably retreated two 
or three miles since these captures, and obsequent’ streams now 
drain the area between the inface and the subsequent streams. 
The rearrangement of drainage, however, has not stopped at 
this point; each master subsequent stream, continuing its head- 
ward growth, has acquired in the most symmetrical manner one 
of the two forks that once belonged to the Petit Morin; the 
northern of the forks (the Somme) now flowing northward to 
the Marne; the southern of the two (the Maurienne) south- 
ward to the Aube-Seine; the distance from the elbow of cap- 
ture to the master river being almost the same in the two 
cases. Inasmuch as a long time must have elapsed between 
the early beheading of the Surmelin and the Grand Morin and 
the later beheading of the Petit Morin, the latter stream had 
time enough to cut a valley of considerable depth through the 
upland before it was beheaded. But now, in consequence of 
its loss of volume by the diversion of its headwater forks, its 
diminished lower course is embarrassed by the rock waste that 
creeps down the slopes of its steep-sided valley in the upland, 
and hence its present head is converted into a marsh—the 
marais de St. Gond—for several miles. Here a local peat 
deposit has been formed; it is now excavated for fuel, thus giv- 
™See (London) Geographical Journal, V, 1895, 134. 
