160 



Scientific Geology. 



their place. The water worn appearance of those rocks, in every 

 part of the State, which are undergoing no disintegration at their 

 surface, must, it would seem, arrest the attention of a very careless 

 observer : although I have been surprised to meet with so few men 

 who have noticed the fact. In some cases, however, the rocks are 

 not merely smoothed, but are grooved and furrowed, as if heavy and 

 irregular bodies had been dragged over their surfaces. The follow- 

 ing sketch exhibits a rock of this description near the turnpike, from 

 Boston to Chelmsford, near the line between Bedford and Billerica, 

 and^ot far from the sixteenth mile stone from Boston. The rock is 

 intermediate between gneiss and mica slate. Its strata seams run in 

 the direction a, a ; and the grooves and scratches in the direction b, b. 



Diluvial Grooves in Gneiss : Billerica. 



The direction of these grooves is nearly north and south ; and this 

 is their general course in every part of the State, east of Hoosac 

 mountain. Commonly, however, they run a few degrees east of 

 south, and west of north. I shall first mention several localities 

 where these furrows correspond in direction to this description, and 

 then notice a few in the west part of the State. 



One hundred rods east of the village on Fall River, in Troy, are 

 grooves and scratches on granite. Some of the bowlders lying on 

 the surface here will weigh from 50 to 100 tons. 



Similar grooves occur on a road leading from the south part of 

 Scituate to Hanover four corners. The rock is granite. 



Also in Abington, Randolph, Canton, Sharon, Dedham, and Do- 

 ver ; on granite and sienite ; very common. 



Also on the conglomerate in Dorchester. 



In passing from Worcester to Berlin, through Boylston, the. like 

 appearances present themselves frequently on the surface of the gneiss 

 and mica slate. 



