324 RECENT CHANGES OF LEVEL 



1. Massive drift lying in patches which show themselves to be fragments of a Ijed of 

 great thickness, left hy the old ice sheet as it melted awa}^ This drift is at the base of the 

 detrital accumulation, and is quite without traces of stratification in its most chai'acteristic 

 sections. A large part of the pebbles are scored by glacial scratches. 



2. Terrace beds of glacial materials rudely distributed by water ; the scratches gener- 

 ally worn away from the surface of the pebbles ; the whole indicating one or more paiises 

 in the re-elevation of the country after the passage of the glacial ice. 



3. A secondary glacial series indicating a recurrence of local glaciation after the partial 

 re-elevation of the country. These secondary glaciers about Boston occupied only the 

 larger stream beds, being traceable in the Charles, the M_ystic, and the Neponset Vallej's. 



4. The rearranged beds lying within a few feet of the present level, which indicate a 

 long continued rest of the sea at or near its present place. At this level the life-bearing 

 beds come again into prominence. 



5. The extensive mud beds and marshes always colored by, and generally in the main 

 composed of, the remains of animals and jjlants. 



There is good reason to beheve that the shore line at Boston has stood at a level some 

 feet above its present position. Near Lynn, on the shore inside of Nahant, is a forest bed 

 lying some feet below high-water mark, covered indeed save at the lowest w^ater. In exca- 

 vations made near Cambridge, coniferous trees have been found with their i-oots in place, at 

 a foot or more beneath low-tide mark. This recent subsidence is ajiparently arrested, if it 

 has not been partly overcome, by a movement in the contrary direction. All the evidence 

 derived from the changes of the coast since the beginning of the historical period, clearly 

 point to this conclusion. 



As we go northward from Boston, as fur as the Merrimac, we find essentiallj' the same 

 features as about Massachusetts Bay. The area of tiible drift which 1 take to indicate a 

 period of submergence, increases as we go to the northw^ard. The altitude to which this 

 attains seems to become greater Avith the increase of area. The depths of the fiord 

 depressions become continually greater ; streams of small size occupy larger cuttings than 

 in the country about Boston. Along a part of this stretch of shore extends a narrow 

 island. This striji of land seems entirely composed of drift materials, and appears to be 

 made up of the partly rearranged materials of an ancient moraine laid down during the 

 secondary glacial period, indicated in the neighborhood of Boston by the beds marked No. 

 3 in the preceding list. The Merrimac would naturally have been the seat of great local 

 glaciation during this time of renewed ice action. Draining a much larger and higher 

 region than the Charles anil the Neponset, we should naturally expect the moraine phe- 

 nomena arising from this secondary ice action to be much greater here than about the 

 mouth of the lesser streams. No evidence has yet been adduced concerning the latest and 

 most limited movements of the shore line at the mouth of the Merrimac. All that can at 

 present be determined is that the depression at the close of the glacial period was greater 

 at this point than near Boston, and that the secondary glaciation which came after the res- 

 toration of the shore to very near its present level, AS'as more extensive than at points forty 

 miles further south. 



From the mouth of the Merrrimac to Portland, the increase of the (able drift is a very 

 marked feature in the ph3^siognomy of the shore section. 1 have seen none of it below fifty 

 feet in height ; its stratification remains, however, as indistinct as about Boston. At Port- 



