Geology and Mineralogy. ae 
of volatile matter present is large enough to convert the glass, 
when heated to whiteness, into cauliflower-like masses which are 
true pumice. The same author in a later paper ‘‘ On the volcanic 
rocks of the Northeast of Fife, Scotland,” states that a dacite- 
glass, when carefully dried at 110° C. and then weighed was 
found, on ignition, to have lost 8.90 p. c. of its weight ; and when 
fragments were heated in a flame urged by a powerful blast they 
swelled up into cauliflower-like excrescences, 8 to 10 times the 
original bulk. The obsidian of Krakataé (a porphyritic enstatite- 
dacite glass) acted in the same way, yielding a dirty-white 
pumice, “almost undistinguishable from the natural pumice which 
was ejected from that volcano during the great eruption of 
August, 1883.” The latter paper is in Q. J. G.“S., Aug., 1886.- 
6. North America in the Ice Period; by J. 8. Newsrrry. 
(Pop. Sci. Monthly, Nov. 1886).—Dr. Newberry reviews in this 
paper, the facts with regard to the general distribution of the 
drift in North America and illustrates the subject by two maps, 
one of North America, and the other of the United States east of 
the Rocky Mountains. He also gives the results of his personal 
observations, especially in Western America. His map represents 
glaciers as descending along the Rocky Mountains to the northern 
part of New Mexico, and to about the same parallel on the Sierra 
Nevada. The conclusions drawn from the facts are the following: 
that the North American ice envelope covered nearly or quite half 
of the continent; that the Ice period was a cold period; that it was 
a result of general and not of local causes, of cosmical agencies, and 
not of topographic or even terrestrial. With regard to the view 
that no lowering of the temperature in the glacier regions was 
necessary to explain the facts, Dr. Newberry mentions as one 
among many facts, that on the Cascade Mountains, Oregon, pre- 
cipitation of both rain and snow is at present very copious, the 
snow-line falling to 7,000 feet above the sea-level, and yet there 
is no ice where great glaciers formerly existed; the precipitation 
remains; the snow-fall remains; but the glaciers are gone “ be- 
cause of the high annuai temperature.” A depression of tempera- 
ture which should cause the rain-bearing winds from the Pacific 
to do all thé year what they now do only in winter, that is, heap 
up snow on the highlands”—would make an annual accumulation ; 
and thus “the slopes and valleys would soon be occupied by 
glaciers as they were in former times.” 
7. Geological map of the United States; by C. H. Hircucock. 
—Professor Hitchcock has a paper, accompanying a colored geo- 
logical map of the United States, in the Transactions of the Amer- 
ican Institute of Mining Engineers. The map measures 18 inches 
by 28. It is based, as is stated, on the map published in the 5th An- 
nual Report of the Director of the U.S. Geological Survey, prepared 
by Mr. W. J. McGee, and isintended “to illustrate the schemes 
of coloration and nomenclature recommended by the International 
Geological Congress.” The map is handsomely printed (by J. 
Bien) and the effect of the arrangement of colors is excellent 
