272 



There is one rock in Hinghani which is so unique and 

 strikinsj: in its litholoo^ical character and so restricted in its 

 distribution in situ as to give its distribution in bowklers or 

 gkxcial erratics a special interest. This is the red felsite in the 

 vicinity of Bradley Hill, on Lincoln and Thaxter Streets. 

 The accompanying map (PI. 12) shows the distribution of 

 this beautiful rock in the drift, so far as it has been traced out. 

 Tlie bowlders of red felsite are of frequent occurrence nortli of 

 the railroad ; but beyond a mile from Bradley Hill they are 

 few and far between, as indicated by a careful scrutiny of the 

 stone walls, and every observed example has been noted on the 

 map. The bowlders undoubtedly extend farther to the south- 

 east than I have traced them ; but their lateral limits are indi- 

 cated at least approximately by the two lines on the map 

 diverging southward from Bradley Hill. The directions of these 

 lines are approximately S. 23° E. and S. 67° E. The initial 

 breadth of the included area measures the probable east-west 

 extent of the red felsite in situ; but the constantly increas- 

 incj breadth southward must be attributed to the natural fanning- 

 out or radial dispersion which has been noted in other cases 

 of the derivation of o-lacial erratics from a limited area. The 

 mean of the two lateral limits stated above (S. 45° E.) may 

 be regarded as an approximation to the normal direction of 

 glacial movement in Hingham ; or, perhaps it would be better 

 to say the average direction, since it is probable that the trend 

 of the ice-sheet was not at any point constant in dii'cction. 



The fact, that, although the red felsite erratics have been found 

 near the southern end of Main Street, none could be found on 

 the line of or west of this street, is an indication that the 

 movement of the ice was not rectilinear ; but, as shown by the 

 drumlins and glacial striae, it was first east-southeast, changing 

 gradually southward to south-soutlieast, and describing a curve 

 of which Main Street is the chord. Probably, also, tlie 

 movement was, as previously explained, more easterly during 

 the earlier and later stages of glaciation, when the icc-slieet was 



