274 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
competent to the task could he found. It is not possible for me at 
present to review all the new material pertinent to the whole 
problem; attention can be given here chiefly to a few examples 
under the third heading. . 
A Glaciated Valley in Central France. — It is evident that, if it 
were possible to obtain a definite idea of the preglacial topography 
of a glaciated district, the amount of glacial work might be readily 
determined as the difference between the preglacial and the present 
form; independent evidence sufficing to prove that general denu¬ 
dation of the rocky crust in the brief postglacial epoch had been 
inconsiderable. This method leads one to conclude that in gen¬ 
eral the topography of southern New England has not been 
strongly modified by glacial action ; for we find here on the whole 
the same maturely dissected upland that prevails in regions of simi¬ 
lar structure outside of the glacial boundary; the uplands being 
explained as parts of an uplifted peneplain of late Mesozoic date, 
and the valleys as the work of ordinary erosion in a part of Terti¬ 
ary time: but this method of measuring glacial erosion by dating 
topographic forms had not been developed twenty years ago. 
Strong glacial erosion may, however, be expected in New England 
where ice motion was locally accelerated, as through the notches 
of the White Mountains. Again, in the glaciated area of the Cen¬ 
tral Plateau of France, I had opportunity in January, 1899, of 
seeing a valley that had been locally modified to a determinate 
amount by a glacier that once descended northwest from the 
Cantal along the valley of the Rhue to the junction of the latter 
with the Dordogne. Outside of the glaciated area, the valleys of 
the plateau —an uplifted r and sub-maturely dissected peneplain, 
mostly of crystalline rocks — frequently follow incised meandering 
•courses, in which the steep concave slopes are regularly opposed to 
the gentler convex slopes; the latter being spur-like projections of 
the uplands, advancing alternately from one and the other side of 
the valley. Valleys of this kind are singularly systematic in form, 
as the result of the combined downward and outward cutting by 
their streams which, already winding or meandering when the 
erosion of the valleys began, have increased the width of their 
meander belt while they deepened their valleys. On entering the 
glaciated valley of the Rime, it is found that the regularly descend¬ 
ing spurs of the non-glaciated valleys are represented by irregular 
knobs and mounds, scoured on their up-stream and plucked on the 
down-stream side; and that the cliffs formed where the spurs are 
