326 RECENT CHANGES OF LEVEL 



ing here. In the neighborhood of Boston these local glaciers left their moraines at a few 

 feet above the sea level. When they retreated from this position they wasted rapidlj^, 

 leaving no distinct moraines in the upper part of the river basins. It is true that about 

 Mount Wachusett, at heights of over seven hundred feet above the sea, these ice. marks are 

 found again, but the changes required to carry the ice in the valleys back from the sea to 

 heights of near one thousand feet must have taken place with great rapidity, so that no 

 moraines were left. During the return of the ice the glaciers would have pushed their 

 moraines far bej'ond the shore line on this part of our coast, so that they would have soon 

 been wasted away by the sea. None of the elevations near here give favorable points for 

 observation concerning the later stages of the ice retreat. Among the Camden Hills, how- 

 ever, I found several traces of local glaciation, going to show that the ice lingered there as 

 it did on the flanks of Wachusett, only at a somewhat lower level ; the point of arrest in 

 the former locality seeming to be ahont two hundred feet lower than in the Massachusetts 

 Hills. This is explained by the more northerly position of this region. 



The drift at Belfast lies in a nearly unbroken slope, extending from a point about two 

 hundred and fifty feet above the water down to near the tide mark. There can be little 

 doubt that the sheet of drift was once of quite uniform thickness over the floor of the Bay 

 and surrounding country. The action of the sea during the time of depression at the close 

 of the glacial period, leveled off" the surface and partially stratified the materials. The 

 work of rearrangement of a glacial mass by water action, can only go on at the period of 

 contact of sea and land. Under the influence of the strong tides which sweep the shore, 

 pebljles as large as walnuts can be carried for great distances down descending slopes, but 

 larger masses cannot be moved except Ijy the agency of the waves. The work began at 

 the point of greatest depression, when the sea line was about two hundred and fifty feet 

 higher than at present, and has been continued step Ijy step as the sea retreated down the 

 long slope. Naturally the action of the weather has done something to obliterate the suc- 

 cessive stages of this great movement of the sea, but enough remains to enable us to make 

 some important general conclusions concerning the way in which the change came about. 

 In the first place it is to he noticed that there are nothing like distinct terraces on this drift 

 slope, which would justify us in supposing that the elevation took place very steadily and 

 rapidly without the long pauses which would be required to make terrace marks strong 

 enough to endure. The amount of aerial erosion which has acted upon this partly ar- 

 ranged drift, is seemingly about equal at all levels from the base to the summit of the slope. 

 Without attaching very much importance to this sort of evidence, it may fairly entitle us 

 to suspect that the time occupied in the change which carried the sea through a vertical 

 movement of two hundred and fifty feet was relatively very short indeed. It is quite clear 

 that the time required to cut the scarp which marks the present shore has never been 

 given to the work of terrace making at any point between the point of greatest depression 

 and the present shore line. 



As I shall discuss the general relations l^etween the glacial action and the hydrography 

 of the State of Maine in another part of this report, it will not he necessary at this point 

 to give any study to the form of the great basin of Penobscot Bay. I therefore pass at 

 once to the east side of the Bay. 



In the neighborhood of Castine, and along the shore to the southward, the deposit of 

 drift is much thinner than in the neighborhood of Belfast. This is clearly due to the dif- 



