90 



GEOLOGY OF THE SECOND DISTRICT. 



and continually diminished till it nearly thinned out. This kind of wedge-form shape or pro- 

 jection is very common in all collections of ore : it is often called a horse, by miners ; though 

 it is to be distinguished from a dyke, vviiich is also called by the same name ; the latter is 

 trap, or greenstone, and cuts obliquely through the ore from side to side ; but the former is 

 composed of the same material as the rock, and is merely a projecting part of the same. A 

 fact worthy of notice, and which may be given in this connection, is the appearance of small 

 garnets adjacent to strings of ore which branch out from the mass, fig. 23. The shaded part 



is hypersthenc ; and the iron ore is represented in thick black contorted branches, and the 

 garnet appears in the dotted border of ore. Whether the garnet is any way connected with 

 the origin and former state of the magnetic oxide, cannot be determined, but geologists are 

 in the habit of regarding analogous phenomena in this light. 



Original Formation of Masses. 



Masses of ore appear to be coeval with the rock which encloses them ; or, such a view 

 Comports best with many facts and phenomena which are brought to light in mining. If this 

 is sustained by future investigations, it will necessarily follow, that the original formation 

 must have been influenced by the same agents as those which were concerned in the produc- 

 tion or modification of the materials composing the rock. The rock which encloses the ore 

 is clearly unstratified ; from which fact we are also to infer the igneous origin of the inclosed 

 mass ot ore. We are clearly driven off from every other mode of formation : the theory of 

 electro-magnetic agency appears out of the question. The subject, however, must remain 

 open to future investigation. The time will come when these mountains of ore will be laid 

 open, and their structure more perfectly revealed, and the relation subsisting between the 

 rock and the ore disclosed to the light of day. We wait till then for a satisfactoiy solution of 

 this interesting and important problem. 



For a general view of the masses of magnetic oxide at Adirondack, I refer the reader to 



