BASIN OP SEBAGO LAKE. 239 



the region of tlie osar -plains. As employed in tins i'e23ort, the word "sys- 

 tem" denotes the gravels deposited by a single glacial river with its 

 branches, both delta and tributary. According to this nomenclature, 

 almost all of the vast gravel deposits of southwestern Maine are connected 

 as a single system. The word "series" will therefore be used to designate 

 a single line or branch of this wonderfully complex network. An inspec- 

 tion of the map will give a far better idea of these reticulations than a 

 verbal description could give. In some cases it is easy to determine which 

 way the water flowed that formed the transverse lines of gravel connecting 

 the north-and-south series, but often this is diflicult or impossible. Some- 

 times the flow has probably been alternately in opposite directions. 



NOTE ON THE BASIN OP SEBAGO LAKE. 



Sebago Lake is said to have a larger water surface than any other of 

 the Maine lakes. It is interesting in many ways. It occujDies a broad 

 north-and-south valley, which is a rock basin if the depth of the lake is 

 correctly reported at 400 feet, or even if it has half that depth. One who 

 stands on the high hills of Waterford and looks south along the deep, almost 

 V-shaped valley which reaches southward through Harrison and then broad- 

 ens into the beautiful valleys containing Long- Pond and Sebago Lake, will 

 see that here are some interesting questions in structural geology. From 

 the standpoint of the glacialist the region is no less interesting. Several 

 valleys converge toward the basin of Sebago Lake, down which the ice 

 could continue to flow long after the general movement across and over the 

 higher hills had ceased. From the north the ice could easily flow down 

 the valley of Long Pond, also down that of the Crooked River, From the 

 northeast the ice could easily flow from Raymond, Casco, and Thompson 

 Pond along the valleys where lies the Casco- Windham system of glacial 

 gravels, while a broad valley from near South Bridgton would allow a flow 

 from the northwest. The valleys would in fact contain their local glaciers, 

 and these would coalesce in the basin of the lake to form a single mer de 

 glace, which, during the final melting, would retreat less rapidly than the 

 ice in adjoining regions so situated that the flow of the ice from the north 

 was more thoroughly cut off by liigh transverse hills. There are in Maine 

 several places where the ice probably met the sea, and terminal moraines 

 were formed at the ice front. These are: (1) At Readfield Village; (2) on 



