1875.] 393 [Dodge. 



stone beds or veins, as at Newburyport, Nahant, Stoneham, Saugus, 

 and Walpole, and Smithfield, R. I. These are generally more or 

 less magnesian, and beds of steatite are sometimes associated with 

 them. Nephrite occurs at two of these places, Stoneham and Smith- 

 field. Serpentine, usually with asbestus, is found in several locali- 

 ties. Epidote and prehnite are common. Gold, silver and lead have 

 long been known to occur in small quantities, and now seem likely 

 to prove very plentiful at Newbury. Other deposits of these valu- 

 able metals may probably be found. 



How far lithological character can be made a test of age for these 

 extensive and widely distributed crystalline masses of early rocks, 

 now often roughly classed as Laurentian, Huronian, etc., remains to 

 be determined. The term Silurian was once quite as vague, but 

 recent discovery has now limited it to a comparatively small part of 

 the strata to which it was formerly applied, by making necessary the 

 invention and use of new names to designate newly distinguished 

 groups. Perhaps we may also hope for a more accurate knowledge 

 of these primitive metamorphic rocks and consequent more definite 

 use of the names applied to them. The terminology now in vogue is, 

 no doubt, definite and accurate where it was first locally applied, but 

 as carried elsewhere, frequently means little. 



These crystallines occupy distinct bands separated by more recent 

 rocks collected in the area between them. The largest band is 

 bounded on the south and east by a line running from the shore in 

 Lynn; across Saugus and Revere; Maiden, north of Salem St.; and 

 Medford, to the foot of Mystic Pond. Here a valley interrupts the 

 line, which begins again in Arlington, west of Spy Pond, runs 

 through Belmont, west of Pleasant and Forest Streets, swings west 

 to the north and west of Waltham village, crossing Beaver Street 

 about midway of its length, and follows South Street and the Boston 

 and Albany Railroad through Weston into Needham. 



Another band, which includes the Moosehill range of Sharon, lies 

 south of a line extended W. 20° S, from Minot's Ledge Light through 

 Cohasset, south of Hingham village and Weymouth Landing, north 

 of Little Pond in Braintree, by the south shore of Great Pond, north 

 shore of Reservoir Pond in Canton, north of Canton Centre, and 

 from there south-westerly. This band is probably about seven miles 

 wide, but I have not traced its southern limit. 



Between these two, there is a third band more difficult to define. 

 The conformation of the hills in Dover makes it appear to join the 



