Theoretical Considerations. 



349 



bonate at Sterling, as well as at Worcester, are very much curved and 

 commonly reddish white. These ores at Sterling constitute beds in 

 mica slate, whose direction is several degrees east of north, corres- 

 ponding to the general direction of the range. The dip at the mines 

 is 60° to 70° west. 



The above ores need a careful analysis : for it is well known that 

 in other places they sometimes contain a considerable proportion of 

 silver and gold. 



The micaceous oxide of iron described in the first part of the Re- 

 port as in Montague, is in veins traversing mica slate and granite, 

 chiefly the former. But I have nothing to add to the description 

 which I have given of these veins. 



Sulphate of iron is not uncommon in small quantities on the mica 

 slate of this State. 



The only remaining mineral to be noticed in the mica slate of Mas- 

 sachusetts, is the red oxide of titanium. It is very common along 

 the eastern margin of the Hoosac Mountain range of mica slate ; oc- 

 curring in four or eight-sided prisms, generally striated and often 

 geniculated. It is usual to find it associated with zoisite, as at Ley- 

 den, where numerous specimens have been found. Sometimes it pen- 

 etrates quartz and sometimes is connected with hornblende. In Shel- 

 burne I found it in distinct crystals in the mica slate, without any 

 other mineral. I have found it likewise in Colrain and in Conway. 

 At the latter place I found one or two geniculated prisms, more than 

 an inch thick ; also in small crystals having the primary form, that 

 is a right square prism. It is found also in Williamsburg, Chester- 

 field, Middlefield, &c. In Chesterfield I found a small quantity of 

 what I take to be the titanite, or ferruginous oxide. 



Specimens of the greater part of the minerals that have been de- 

 scribed above will be found in the collection which is placed in the 

 hands of government. To procure every one of those, which have 

 been described as occurring in the State, if not impossible, would re- 

 quire so much of time and expense, that I have not felt authorized to 

 attempt it without special directions. 



Theoretical Considerations. 



The prevailing opinion among geologists until recently has been 

 that mica slate and all the older primary rocks have been deposited 

 from a chemical solution of their materials in water. But this opin- 

 ion appears to labor under insuperable difficulties. It seems to me 



