82 thp: butterflies of xew exgland. 



New England beneath the waters of the ocean. In geologically recent 

 times there has been a slight recovery from the depression, enough to lift 

 certain postglacial, marine deposits, that smooth over and simplify the 

 littoral topography, two hundred or more feet above the sea in Maine, and 

 less along the southern coast ; but not nearly enough to reveal all the 

 previously submerged area. A slight submergence of even later date is 

 also inferred. The present shore-line is therefore of complex origin. The 

 great bays and fiords of Maine, Massachusetts and Rhode Island and the 

 fiord-like channel of the lower Hudson River may be considered as old, sub- 

 merged valleys and lowlands, eroded chiefly by the ordinary subaerial forces 

 during the former greater elevation of the land, and finished off by glacial 

 rubbing to an unknown amount : the simpler shore-line of New Hampshire 

 and southern Maine, of southern Massachusetts and Connecticut, results 

 from a j)lentiful supply of drift, with which the depressed and buried low- 

 lands and valleys have there been smoothed over ; many of the smaller 

 indentations on these parts of the coast have been enclosed by bars of sand, 

 brought by the waves chiefly from drift-bluffs near by ; the shallow waters 

 behind the bars have commonly been filled up to high-tide level as salt- 

 marshes. The cliffs and bars that mark the present shore-line are much 

 more distinct than any that remain at a higher level. 



On a surface thus slowly prepared by many processes, standing in an 

 attitude thus lately gained after many oscillations, the present rivers and 

 streams have, as it were, just begun their new, postglacial tasks. The 

 little headwater streams of the mountainous districts still for the most 

 part follow their steep, preglacial ravines. The larger rivers, like the 

 Connecticut, and those smaller ones that are hedged in by steep-sided val- 

 leys, like the upper Androscoggin or the Westfield, follow closely along 

 their old courses, although somewhat disturbed by the drift-filling in which 

 they have now sunk their channels : and what with northern elevation 

 whereby the river-slopes are steepened and the base-level lowered, and 

 what with the present slower washing away of the plant-covered drift- 

 surface, whereby the ratio of load to water-volume is decreased, the rivers 

 have been empowered to carry away the detritus that they had shortly 

 before deposited ; and thus are formed the terraces that make so charactei- 

 istic an element of our valleys. The terracing process probably advanced 

 rapidly as long as the rivers found only clay and sand to cut away, for 

 even in the brief postglacial period since the work began, that share of it 

 is very generally accomplished. Further terracing will be accomplished 

 much more slowly, for the deepening of the channels is now retarded by 

 rocky ridges and spurs which nearly all the streams have discovered in 

 opening their buried valleys ; it Avoidd have required more foresight to 

 avoid these obstructions and settle down precisely on the lowest line of the 

 old valley than can be expected of rivers. When a rocky ledge is thus 



