POST-TERTIARY PERIOD. 539 



Monadnock (Hitchcock). They are (2) thickly crowded over 

 large areas, as if the whole had been under friction from, a mass of 

 material which spread over and covered it. At the same time, 

 (3) the variations from broad smooth planings and ploughings to 

 deep groovings and fine scratches show variations in the moving 

 mass. Also (4) the channels are sometimes made of broken lines, 

 or a succession of slight curves, as if from hitches in the progress 

 of the gouging agent ; and, coming to the edge of a layer where 

 there was a sudden descent, they have occasionally chipped it off, 

 as if the heavy body had gone down with a jump. 



Again, (5) broad surfaces have been smoothed or polished by the 

 same agency, and exposed rocky ridges have been rounded, pro- 

 ducing smoothly rounded knolls or hummocks, like what are called 

 roches moutonnes in the Alps. 



Direction of the groovings. — Again, (6) the groovings have a general 

 southward direction, varying mostly between S. 20° W. and S. 20° E. 



In New England the most common course is about S. 10° E. In central 

 Massachusetts, between S. 8° E. and S. 15° E. ; in eastern, about S. 20° E. ; in 

 the Berkshire Mountains, S. 50° E. ; about Mount Washington, S. 18° E. ; in 

 Vermont, S. 10° E., but varying between S. 80° W. and S. 75° E., or, omitting 

 exceptional cases, between S. 25° W. and S. 25° E. On the west side of the 

 Green Mountains the course is mostly within a few degrees of north and south. 

 It is the same in eastern New York. 



In Maine the courses have an unusual amount of easting. According to the 

 observations published in the Geological Report of C. H. Hitchcock, sixty-six in 

 number, they vary between S. 80° W. and S. 70° E., but excluding three, be- 

 tween S. 17° W. and S. 60° E. ; and about a fourth of all are between S. 40° E. 

 and S. 70° E. 



In western New York the course is mostly southwest; in Ohio, generally 

 southeasterly, and the same in the larger part of Michigan and Illinois; in 

 Iowa and Wisconsin, and over the country to the Lake of the Woods, from the 

 northward. In northern Michigan the courses vary between W. by S. and S.W. 



Two or more sets of groovings. — There are (7) frequently two or three 

 sets of groovings, differing a little in direction. Thus, in western 

 New York there is, in addition to the northeast system, a subor- 

 dinate north and south system (Hall). On Isle La Motte in Lake 

 Champlain there are eight sets (Adams), although usually not over 

 two or three in Vermont. 



Groovings on elevated summits. — Again, (8) the scratches are found 

 on the heights as well as lower lands. They occur to a height of 

 5000 feet on the Green Mountains (Hitchcock) ; on the top of Jay 

 Peak, 4000 feet high (Adams) ; on the top of Monadnock. In 

 some instances (9) the wear and scratches are most decided on the 

 north side of elevations. Professor Hitchcock has observed that 



