202 'Tin American Geologist. September, 1893 
scribed. On the contrary, then- is an abundance of them scattered all 
over the submerged parts of Maine. I have described them under the 
name of glacial marine deltas.* They vary in size from one-fourth of a 
mile in diameter up to areas of 100 or more square miles. The structure 
of the larger deltas is often complicated, since sometimes more than one 
glacial river helped to form a single confluent delta, and sometimes a 
portion of a delta was deposited in a glacial lake which ultimately be- 
came a bay of the sea by the melting of the ice on the seaward side. 
There are in the state dozens of these deltas each having areas of four 
square miles or more, and often they are kuown to attain a depth of 
more than 100 feet in places. At intervals of five to twenty miles most 
of the longer osars expand into marine deltas separated by reaches of 
gravels deposited between ice walls and showing no tendency to spread 
into delta form. The successive deltas found in the course of a single 
glacial river form an important aid in mapping the approximate posi- 
tions of the ice-front at different periods of the recession of the ice. Sev- 
eral of the osars expand into three, and one into perhaps five, of these 
retreatal deltas. At their landward ends the glacial marine deltas con- 
sist of reticulated ridges of coarse water-rounded matter, boulders, 
boulderets and cobbles, with coarse gravel. Going southward the ridges 
become broader, confluent at their bases and lower, and finally merge 
into a rolling plain which, in the larger deltas, becomes at last quite 
level. At the same time the material becomes gradually finer, passing 
from gravel to sand and finally clay. At the proximal ends of the del- 
tas the foesiliferous marine clays cover the gravel ridges or their flanks, 
and were plainly deposited later than the coarse gravels. Distally 
the delta clay passes by insensible gradations into fossiliferous clay 
which is stratigraphically continuous with the delta, and therefore must 
have been deposited simultaneously with it in the open sea. I know of 
no instance of continuous deltas, that is, such as would be formed off 
the ice front during a continuous retreat of the ice and the uninter- 
rupted flow of a glacial river, bringing sediments into the sea all the 
time of the retreat. These and many other details complicate the ques- 
tion of interpretation, and in a brief article only a small part of the facts 
can be discussed. 
The deltas here referred to are retreatal glacial deltas, formed subse- 
quently to the osars of the coast itself and while the ice front was re- 
treating over the then submerged region lying north of the present 
shore. They are an essential part of the development of the osars and 
show all the signs of matter swept by glacial rivers into the sea, where 
the currents were gradually checked. Both in their topographical and 
stratigraphical relations they are very different from the fluviatile del- 
tas that were at a later period brought into the elevated sea of that 
time by the present rivers, when they first began to flow. In the inte- 
rior of the state, in consequence of the greater differential postglacial 
elevation of the land toward the north and west, these fluviatile deltas 
♦Classification of the Glacial Sediments of Maine, American Journal of Science, 
August, 1890. 
