152 The American Geologist. September, i'j(.4 
thirty years ago, drawn from the Delaware river at Trenton, 
N. J., to the lower part of the Kansas or Kaw river, with the 
maps of it pnblished by Chamberlin in 1883 and 1888,* the 
former reaching Avestward to the east edge of Montana, but 
largely revised and corrected for all the country northwest 
of the Kaw river by his next map five years later, we are 
greatly impressed with the rapid progress of our American 
explorations of the limits of glaciation, which were traced ex- 
actly or approximately through the distance of more than 3,000 
miles across the continent between thirty and fifteen years ago. 
A principal incentive to that work was the recognition of 
the terminal moraines of our continental ice-sheet, in the vears 
1877 to 1880, by Cook and Smock in New Jersey; by the 
present writer on Long Island, Block island, ^Martha's Mne- 
yard, Nantucket, and Cape Cod; by Lewis and Wright in 
Pennsylvania and Ohio ; by Chamberlin in Wisconsin ; and 
b}' N. H. Winchell and the writer in ^Minnesota, Iowa, and 
South and North Dakota. \\'ithin three years after the first 
mapping of the marginal moraines in New Jersey, they had 
been mapped more or less exactly for 2.000 miles from south- 
eastern Alassachusetts to where their course passes out of the 
United States, from North Dakota into ^Manitoba and Assin- 
iboia. 
About a quarter of a century has since passed, and very 
detailed surveys of the glacial drift and its extreme margin, 
and of the manv parallel and interlocking or overlapping mo- 
raines which limit the areas of the ice-sheet at successive 
stages of its recession, interrupted here and there by re-ad- 
vances, have been made by numerous observers in southern 
New England and Long Island ; by Salisbury in New Jersey ; 
Wright and Leverett in Ohio. Indiana, and Illinois; Cham- 
berlin and Salisbury in Wisconsin ; Calvin and ^^'inchcll and 
their associates on the geological surveys of Iowa and Minne- 
sota; and Todd and the present writer in the Dakotas. 
Farther westward little thorough work has been yet done, 
though important reconnaissances, a'.\d detailed studies in 
* Five maps in Preliminary Paper on the Terminal Moraine of the Second 
Glarial Epoch, (.pp. 291-402),'7V2irrf Annual Report of the V. S. Geol. Survey, 
for 1881-2, pub. 1S83. Map of the Glaci.nl Strijc of the eastern I'uited States 
(and of the Earlier and Later Drift across all the northern states), in The 
Rock-Scorings of the Great Ice Invasions (pp. 147-248), Seventh Annual Re- 
port, U. S. G. S., for 1885-86, pub. 1S88. 
