118 GLACIAL GRAVELS OP MAINE. 



into clay, within one-fonrth of a mile. This clay is continuous with that 

 which extends clown the valley of Union River to the sea, and is of marine 

 origin, as shown by fossils found about 1 mile east of this place. North of 

 the road we find two tributary branches. One ridge extends for about one- 

 eighth of a mile northwestward, up the valley of a small stream; the other 

 starts from a point a few rods east of this ridge and ascends another valley 

 northward for one-half mile or more. This gravel plain is small, but inter- 

 esting. The horizontal transition from gravel and cobbles on the north to 

 sand and finally clay on the south is shown with unusual regularity and 

 within a short distance. It is an instructive instance of a delta deposited 

 by two small glacial streams, whose mouths were so near each other that 

 they formed a single delta-plain. 



NORTH MARIAVILLE SYSTEM. 



This is a discontinuous series of short ridges and hummocks separated 

 by numerous short gaps, or apparent gaps. On the north the series begins 

 about 1 mile north of North ]\Iariaville and takes a south course along the 

 west side of Union River for several miles. Near the road from Otis to 

 Waltham it crosses to the east side of the river, where the gravel takes the 

 form of a low terrace, while no corresponding terrace is found on the west 

 side of the river and no similar gravel is in the bed of the stream. This is 

 thus proved to be glacial gravel and not valley drift. South of this point 

 the valley of Union River is a very level, clay -covered plain, and no ridges 

 can be seen rising above the clay. Probably the series ends near this place. 



WEST MARIAVILLE MASSIVE. 



About 1 mile from Union River, on the road from North Mariaville 

 southwestward to Tilden Post-Office, is a flattish-topped plain of well- 

 rounded glacial gravel and cobbles. It is about one-fourth of a mile wide 

 from east to west and three-fourths of a mile long. The plain becomes 

 somewhat finer in composition toward the south, but the change is not so 

 marked as it is in the case of most fan-shaped deltas. The plain is but little, 

 if any, broader toward the south. It must have been deposited either in a 

 glacial lake or within a bay of the sea bordered by ice walls that prevented 

 the sediment from spreading. If so, the outlet channel toward the sea was 

 probably narrow. 



