MINERALOGY. 4I 



sediments* Fig. 5 on PL 2 represents one of the most remarkable. It 

 is drawn from a section of a diorite from Connecticut lake. It appears 

 in the microscope as composed of a dark gray, translucent substance 

 traversed by lines of greater transparency ; and nothing could resemble 

 more closely the structure of a coral, or of a fragment of some rhizopod. 

 By reflected light the whole appears white, traversed by faintest black 

 lines. Fig. 6, though less organic in appearance, is fully as remarkable 

 as a decomposition product of titanic iron. It represents a form found 

 abundantly in the diorite of Hanover. Persons are naturally interested 

 in finding organisms in old rocks ; and besides the cautionary value that 

 may be attached to these figures, they are illustrative of a method of 

 decomposition, which, in our greenstones, is characteristic of the titanic 

 iron. 



27. Spinel [Mg AI2 O4]. 



The mineral spinel has been found in pretty little bright red octahe- 

 dral crystals in a limestone rock on Saddleback mountain, 



28. Magnetite [Fcg O4]. 



This ore is found in deposits of such magnitude that efforts have 

 been made to mine it. It is widely distributed in smaller amounts. At 

 the Franconia iron mine, in Lisbon, there is a vein from 5 to 8 feet thick 

 in the gneiss rock, which was worked for some time. Fine dodecahedral 

 crystals are found there. The ore is compact, fine grained, and of a 

 bluish gray color. Jackson's analysis is as follows : 



Iron proto-sesquioxide, 96.20 



Titanic acid, ........... 1.50 



Silica, 2.30 



When the vein was worked, several other minerals in fine crystallized 

 condition were obtained from the mine, and it was an often-visited local- 

 ity. Garnet, epidote, and hornblende were found in crystals remarkable 

 for their beauty. Magnetite occurs in large beds in Unity ; but in this 



* See Hawes, American Joiirnal of Science, iii, vol. xii, p. 134. The other gentlemen who have seen these 

 specimens, and have published opinions in reference to them, are very excusable, on the ground that they saw but 

 single specimens, and are not professed experts in microscopic mineralogy. The author has paid some attention 

 to the subject, under competent instruction, since the paper referred to was published. 



VOL. III. 6 



