Review of Recent Geological Liter attire. 381 
He ascribes their interrupted deposition near the front of the glaci- 
ated area to subglacial streams. Farther north, as the system length- 
ened, the receding ice-sheet, deeply melted on large areas and cov- 
ered by its previously englacial drift, appears to have become chan- 
nelled by large superglacial streams, open above to the sky and flow- 
ing through occasional broad basins inclosed by the waning ice- 
fields, where the esker ridges are replaced, sometimes for several 
miles, by extensive gravel and sand plains. 
The valley drift of gravel, sand, and clay, once forming continuous 
and thick flood-plains, but now carved in terraces by river erosion, and 
also the marine clays of the coast and of the great valleys up to 200 
or 300 feet above the sea, are shown to have chiefly originated, like 
the esker gravels, from the englacial (and by ablation superglacial) 
drift of the departing ice-sheet. 
Following the classification of Torell in Sweden and of Hitchcock 
and Uphain in New Hampshire, Prof. Stone regards the com.pact and 
hard lower part of the till as a ground moraine, while the compara- 
tively loose upper till, containing fewer glaciated rock fragments and 
an increased proportion of large boulders, is ascribed to deposition of 
drift which had remained in or upon the lower part of the ice until 
the completion of its melting. The quantity of the finally englacial 
drift which became superglacial, falling on the ground as the upper 
lill, is estimated to have averaged generally only a few feet, with a 
maximum of perhaps twenty feet. 
Many very interesting questions concerning the history of the Ice 
age in Maine are most ably and instructively discussed in this mono- 
graph, and it will be read attentively by the glacialists of America 
and Europe. The question of greatest consequence, in a comparison 
of this state with other drift-bearing regions, is probably that w'hich 
asks for evidence of interglacial stages, or great recessions or depart- 
ure of ice-sheet, succeeded by renewal of snow and ice accumulation. 
On this subject Prof. Stone writes as follows: 'Tt is well known that 
in the Mississippi Valley there are two or more layers of till separated 
by strata containing peat and other traces of a warm interglacial 
period. No such signs of two general glaciations have yet been found 
in Maine. The few facts that indistinctly point that way seem as yet 
to be capable of other interpretations, although during the final melt- 
ing there may have been alternate retreat and advance near the ice 
margin." 
Each county of the state is mapped separately, in alphabetic order, 
showing the courses of the esker gravel systems. It would have 
further aided the reader, if a map of the whole state on a small scale 
had been added, noting these .systems, with their names, in a single 
comprehensive view. w. u. 
Th& Illijiois Glacial Lobe. By Frank Leverett. Monographs of 
the U. S. Geol. Survey, Volume XXXVIII. Pages xxi, 817; with 24 
plates, and 9 figures in the text. iSgg. Price, Si. 60. 
This is one of a series of monographs which are being prepared, 
