Range and Extent of Granite. 



47 i 



of granite : but I have thought it useless to attempt to represent them 

 on the map. My opinion is, that in going- easterly the granite in- 

 creases in quantity until the gneiss and mica slate at length disap- 

 pear. 



The Worcester range of mica slate contains numerous large beds 

 or protruding masses of granite; some of them of great interest, on 

 account of their adaptedness to architectural purposes. It must not 

 be expected, however, that in all cases a deposit of granite will be 

 found in the precise place where one is marked on the map, in this 

 mica slate. In Worcester the spot thus coloured is intended to mark 

 out the true situation of an interesting deposit of granite : the only 

 one which I have discovered in the southern part of the mica slate. 

 The spot in Harvard, also, represents a deposit of remarkable por- 

 phyritic granite. In Westford, Lowell, and Tyngsborough, the spots 

 coloured as granite, indicate only that numerous masses protrude in 

 that vicinity. In Pelham, N. H., I intended to mark the bed which 

 is now extensively quarried. In Pepperell, Townsend, and Lunen- 

 burg, I intended only that the beds marked should stand as the repre- 

 sentatives of numerous veins and masses in those towns. The same 

 is particularly true of the spots marked in Leominster and Westmin- 

 ster. In passing from the former to the latter place, granite is very 

 abundant: and the mica slate, sometimes for a considerable distance, 

 disappears. A spot marked in the south part of Fitchburg, is intend- 

 ed to designate the large hill of granite that furnishes so fine a build- 

 ing stone in that town. 



Except in the northwest part, I have colored no spot as granite in 

 the extensive range of gneiss in Worcester county. That it exists 

 elsewhere I doubt not : as on the top of the hill in Spencer, where 

 one sees the granite obviously protruding through the pseudo-gneiss 

 strata: But I believe that much, which in that range has been called 

 granite, is nothing but granitic gneiss. It is only after long experi- 

 ence in examining these rocks, that the difference is perceived between 

 granitic gneiss and real granite. 



In the northwest part of this gneiss range, especially in the lower 

 part of N. Hampshire, we find the gneiss changing into mica slate, 

 with occasional masses of considerable extent of fine grained granite, 

 generally excellent for economical purposes. The beds of granite 

 and mica slate which are there marked, are not intended to represent 

 the exact relative position and quantity of the three rocks, but only to 



