38.S The American GeoJayixt. DfcMnber, i89-2 
(Iril't iiiui IciTiict's. The sixtli cliaplrr Irciits of tiie iiiicieiit fflaciers 
of the Alj)s and other niountaiiis? in the eastern hemisphere and the 
ice-sheets and glacial drift of northwestern Europe, including a very 
interesting description of the drift in Great Britain by Mr. Percy F. 
Kendall, with an excellent contour niaj) of the British Isles. 
In the seventh chapter the clianges of drainage ])roduced by the 
ice-sheets are described, with the formation of a glacial lake in the 
Ohio valley, of the much enlarged Laurentian lakt^s when the receding 
ice was a barrier preventing their i)resent northeastward outHt)W, of 
lake Agassiz in the valley of the Red river of the North and basin of 
lake AVinnipeg, and of thetiuaternary lakes Bonneville and I>ahontan 
in the arid Great Basin of interior drainage. For the parallel roads 
of Glen Roy in Scotland the old explanation is given, ascribing them 
to obstruction by a local glacier, instead of which .Tamieson has shown 
that the glacial hike of Glen Roy was ])eiit u]) by the dei)arting 
Scottish ice-sheet. 
The evidences of man's existence during the glacial period l)()tli in 
Euroi)e and North America are the subject of the eighth chaj)ter. 
For this ct)ntinent tlie author should have added, besides the many 
localities which he cites where stone implements have been found in 
river gravels belonging to the ice age, the three discoveries showing 
man to have been contemporaneous with the great Pleistocene lakes, 
namely, the charred sticks, ashes and stones placed to form a rude 
hearth, found at a depth of about 18 feet under the ridge of beach 
gravel on the shore of theglacial lake, Iroquois, in Gaines township, N. 
Y., which Gilbert. refers to the time of discharge of this lake through 
the Mohawk and Hudson rivers; the chipped fragments of quartzite 
found by Tyrrell in a beach of lake Agassiz; and the obsidian spear- 
liead discovered by ^IcGee in the sediment of lake Lahontan. 
Professor Wright discusses the cause and date of the glacial period 
in the two remaining chapters. Concerning the cause, he agrees 
with Upham and Le Conte that it was probably the great altitude to 
which the glaciated countries had been uplifted during the closing 
stage of the Tertiary era and beginning of the Quaternary, shown by 
fjords and submarine valleys to have been generally 3,000 feet or 
more above their present hight; and concerning the length of the 
Postglacial or Recent period, his observations accord with those of 
N. H. Winchell. Gilbert, Andrews, and others, that probably only 
about 7,000 to 10,000 years have elapsed since Canada and the north- 
ern United States were uncovered from their ice-sheet. The length of 
the Glacial period is believed, as by Prestwich,to have been probably 
no more than 30.000 or 40,000 years. Only one epoch of Pleistocene 
glaciation is admitted by the author ; and the supposed interglacial 
forest beds and other fossiliferous beds between deposits of till are 
attributed to moderate recessions and re-advances of the ice-border. 
This interpretation and some others of the author's conclusions, es- 
])ecially those relating to the cause of the Ice age and its date and 
duration, will doubtless be tojMcs of iiuich further debate by glacial- 
