Jievi'eir of Jiecoit Geoloyical Literature. 55 
Ami'rica, {li'\cl()|)('(l tlif ;;i'cal Ifrmiiial moraines, and lliat tlicsc m<i- 
raincs arc bordered on the ouLside by plains and valley trains of sand 
and gravel, denotini;' more vifi'orous drainage than durinj; the earlier 
stafjres of the ice." Commentinji' on this, the present reviewer would 
in(iuire. May not the close aiin-ement in the lilacial succession on the 
two continents i>e more pr()l)al)ly in each casi' the expression of varyinji' 
physical conditions of the increase, culmination, and especially the de- 
cline, of a single cycle of jilaciation. rather than the records of several 
independent e])ochs of ice accumulation and depjirture? 
Applyinjj: the interpretation of these series of glacial and interglacial 
deposits which seems to find warrant in Russell's observations of tlu^ 
Malaspina ice-sheet in Alaska, covered on its border for a width of sen- 
era! miles with drift on which forests, thickets, and abundant herba- 
ceous (lowering plants of temperate species grow luxuriantly, we maj' 
attribute all the complex secpience of drift formations in Europe, as in 
North Amei'ica, according to tiie opinion of the reviewei', to moderate 
fluctuations of the l)onnd;iries of the ice-sheet, and <;f its waning rem- 
nants, during a coni inuous (jlacial period of i)robal)ly no longer dura- 
tion than :i(),UOO or ."iO.OiiO years. While the ice-sheets were being accu- 
mulated, doubtless a severely boreal and arctic climate prevailed in 
these regions; but when the formerly greatly elevateil lands had sunk 
under their ice burden to their present altitude or lower, a warm tem- 
perate climate was restored, similar to that which now characterizes 
the low latitudes from whicji the ice was l)eing nu-lti'd away. Any re- 
advaiu;e of the ice-l)oi'der would then cover remains of a faunaaud flora 
consisting wholly or ciiielly of t"mperate species. Under this vii'W, the 
time divisions which I*rof. (ieikie calls e[)och9 seem mori' properly to 
be considi'red as episodes or stages in a single epoch or jH-riod of con- 
tinuous though f1uctu;iting glaciation. 
Professor Chamberlin's two chapters contain, in ."i'i pages with two 
maps, a vi'ry comprehensive and valuable statement of the chief fea- 
tui'es of North American glacial geology. In all the grand outlines and 
most of the conclusions, as the explanation of iiraclically all our drift 
pheiioiniMia by lan<l-ice. i he reviewer is in he;ii-ly .accord, so that it is 
almost lri\ial t<i I'efer principally, as in this notice, to the following 
points where he would (lilfer in the inferences fi'om I'ecoriled oi)serva- 
tions. The Laiirentide and ( 'ordillei'an ice-sheets should probably be 
shown as conlluenl ;ici'oss I he low portion of the liocky mountains in 
the region of the Peace ri\i'r and northward: during the maximum 
stage of glaciation. I he greatest thickness of the F.aurenlide ice-sheet 
may ha\(' extended ulong an east to west l)e|| somewhat south of the 
Labradorian and Hndsonian centers of later railiating slriation and 
drift transportation: the northward glacial How from northern New 
England toward t he St . Lawrence, as suggested by ('halmei-s. appears 
to ha\e belonged only to a \ei'y late stage when the melting of the ice 
in the St. Lawrence \ alley, proceeding faster than on the mountainous 
area at the south, left there a large isolated ri-mnaiit of the departing 
ice-sheet: 1 he imbrication or overlappi ng of t he drift si-ries, well illus- 
