306 



EARTH FEATURES AND THEIR MEANING 



gan is found the equally beautiful jaspilite composed of puckered 

 alternating layers of black hematite and red jasper. On Keweenaw 

 Peninsula, which protrudes into Lake Superior from its southern 

 shore, is found that remarkable occurrence of native copper within 

 a series of igneous rocks of varied types and colors. Fragments 



of this copper, some weighing several 

 hundreds of pounds each and masked 

 in a coat of green malachite, have under 

 the name of " drift " or " float " copper 

 been collected at many localities within 

 a broad " fan " of dispersal extending 

 almost to the very limits of glaciation 

 (Fig. 331). 



Some miles to the north of Provi- 

 dence in Rhode Island there is a hill 

 known as Iron Hill composed in large 

 part of black magnetite rock, the so- 

 called Cumberlandite. From this hill 

 as an apex there has been dispersed a 

 great quantity of the rock distributed 

 as a well marked " bowlder train " 

 within which the size and the fre- 

 quency of the dispersed bowlders is in 

 inverse ratio to the distance from the 

 parent ledge (Fig. 332). Similar 

 though less perfect trains of bowlders 

 are found on the lee side of most pro- 

 jecting masses of resistant rocks within 

 the area of the drift. 



Large bowlders when left upon a 

 ledge of notably different appearance 

 easily attract attention, and have been 

 described as " perched bowlders." Resting as they sometimes do 

 upon a relatively small area, they may be nicely balanced and 

 thus easily given a pendular or rocking motion. Such " rocking 

 stones " are common enough, especially among the New England 

 hills (plate 17 B). Many such bowlders have made somewhat 

 remarkable peregrinations with many interruptions, having- been 

 carried first in one direction by an earlier glacier to. be later trans- 



FIG. 332. Map of the "bowlder 

 train" from Iron Hill, R.I. 

 (based upon Shaler's map, but 

 with the directions of glacial 

 striae added). 



