132 G. H. Stone — Glacial Sediments of Jfaine. 



At the same time the lateral slopes of the reticulated ridges 

 become less steep, the kettle-holes shallower, the ridges broader, 

 and thus the plexus of ridges is merged in a rolling plain 

 which becomes more and more even until it is a level plain of 

 nearly horizontally stratified sand and at last clay. The posi- 

 tion of the mouth of the glacial river is shown by the kame or 

 osar extending north from the delta. 



2. Narrow Marine Deltas. — In shape this kind of delta is a 

 long plain a half mile or less in breadth, and expanding but 

 little in breadth toward the south. There is a gradual transi- 

 tion from coarser to finer matter as we go southward and at 

 last the sand ends on the south in the marine clay. But at the 

 sides the northern portion of this plain usually rises abruptly 

 several feet above the adjacent ground. The marine clay here 

 overlies the sand or gravel plain which consists of matter much 

 coarser in composition than itself, proving that the clay is a 

 later deposit than the gravel and sand plain. My interpreta- 

 tion of the facts is that these deltas were formed in wide chan- 

 nels forming bays by which the sea 'extended some miles back 

 into the ice-sheet. At the time of deposition the delta was 

 bordered by ice on each side, while the open sea lay in front. 

 As the channel or bay broadened by the melting of the ice, 

 the parts adjacent became covered by clay, derived from the 

 glacial stream which now was checked in the recently widened 

 channel at a point farther north than previously. 



The transition of the delta sands into the marine fossiliferous 

 clays proves that the latter were chiefly composed of the mud 

 poured into the sea by the glacial streams. I have not been 

 able to find fossils in the clays very near the marine deltas and 

 apparently the inflow of cold, muddy, fresh water exterminated 

 marine life near the mouths of the glacial rivers. The small 

 amount of erosion accomplished by the waves of the sea is 

 elsewhere noted. Eroded till can have furnished but a small 

 proportion of the great sheets of silt and clay, which cover a 

 large part of Maine up to 230 feet. Logically the marine clays 

 ought almost wholly to be classed among the glacial sediments. 

 But the clay portions of the marine deltas of neighboring 

 glacial rivers often coalesce, so too the delta-clays are mixed 

 with some clay derived from till eroded by the waves. Hence 

 it is difficult to map the delta-clays, and for the present T con- 

 fine the term marine deltas to the coarser sediments (gravels and 

 sands) spread over the sea bottom by the glacial streams. Yet 

 it ought distinctly to be admitted that the so-called Champlain 

 clays of Maine are almost wholly a marine off-shore deposit of 

 Gletscher-milch, such as must be forming off much of the 

 Greenland coast to-day. 



8. The broad Osars or Osar-jplains. — All the longer gravel 

 systems of Maine take the form, at the northern ends, of the 



