Some miles to the north of Providence 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 frequency 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 projecting 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 transported in wholly different directions at the time of new ice invasions. ┌───────────────────────────────────────────────────────────────────┐ │ PLATE 17. │ │ │ │ [Illustration: _A._ Soled glacial bowlders which show differently │ │ directed striæ upon the same facet.] │ │ │ │ [Illustration: _B._ Perched bowlder upon a striated ledge of │ │ different rock type, Bronx Park, New York (after Lungstedt).] │ │ │ │ [Illustration: _C._ Characteristic knob and basin surface of a │ │ moraine.] │ └───────────────────────────────────────────────────────────────────┘