258 TJic Aiucricati Geologist. October, i898 
C. H. Flitchcock. It is for the most part a very dark silicious rock, 
the color of which is due to finely disseminated carbon. This forma- 
tion, varying from 2,000 to 5,800 feet in thickness, extends from south 
to north through Vermont; but its most important development, 
ecoromically, is in the townships of Washington and Topsham, 
Orange county, where, within the past five years, numerous valuable 
marble quarries have been opened in it. The chemical composition 
of specimens of the marble from a deep test pit at one of the quar- 
ries is very remarkable, no less than eighteen elements having been 
detected in its analysis. 
9. Fluctuations of North American Glaciation shown by Intergla- 
cial Soils and Fossiliferous Deposits. By Warren Upham, St. 
Paul, Minn. -From a comparison of our continental drift deposits 
with the present retreatal conditions of the piedmont Malaspina gla- 
cier in Alaska, it is concluded that the flora and fauna adjacent to the 
retiring ice-sheet were nearly like those of the same latitudes to-day, 
and that fluctuations of the ice-border to the extent of a few miles, 
a few score, or a few hundred miles, at different stages of the ice age, 
due to moderate secular climatic changes, more acceptably account 
for our interglacial beds, former surface soils and leached subsoils, 
than a general departure and renewal of the ice-sheet. 
No more surprise need be occasioned by the occurrence of remains of 
warm temperate floras and faunas in these beds than we must feel in see- 
ing tropical and temperate plants and animals at the foot of the Himalay- 
as and the Alps. These extensive mountain ranges, frigid and largely 
snow-covered, doubtless exert as much influence on the climate of the 
contiguous valleys and lowlands as could be due to the waning ice- 
sheets of North America and Europe, when the Early Glacial high con- 
tinental altitude was succeeded by the Late Glacial or Champlain de- 
pression of these great areas somewhat below their present level. The 
ice-sheet of each of these continents, in its time of retreat, being wasted 
by a warm climate at its edge, probably rose to an altitude of 5,000 feet 
above the land within 100 or 200 miles back from the ice border, which 
theiefore might considerably readvance during any series of exception- 
ally cool years, with plentiful snowfall. 
10. Time of Erosion of the Upper Mississippi, Minnesota and St. 
Croix Valleys. By Warren Upham. Until the Ozarkian epoch 
of great elevation of the northern part of this continent, inaugurating 
the Quaternary era, the upper part of the present Mississippi basin, 
above the vicinity of Dubuque, appears to have been drained northerly, 
according to recent studies by Hershey (Am. Geologist, XX, 246-268, 
Oct., 1897). After the Cretaceous marine submergence of the state 
of Minnesota, its chief river system probably flowed through the Red 
river valley to Hudson bay curing the Tertiary era, being reversed 
to take nearly the course of the Minnesota and Mississippi rivers at 
the end of that era. The St. Croix river is thought by the author to 
have obtained its passage through the rock gorge of the Dalles at 
