ELY GREENSTONE. 163 



description of some of the contacts of the various formations of the district 

 with the greenstones, in which their relations to one another will be given, 

 will be found under the discussion of these formations. 



ECONOMIC VALUE OF THE ELY GREENSTONE. 



The Ely greenstone rocks of the Vermilion district are suitable for 

 building stones, especially for foundations, for which the unworked stones 

 can be used. They are very tough, and there is hardly sufficient demand 

 for stonework to warrant their being cut and used for the superstructure 

 of buildings, even if their color were suitable. Their color is, however, 

 uniformly so dark that they would rarely be used for other portions of 

 buildings than foundations and trimmings. This stone is eminently adapted 

 for use as road material, as there is an inexhaustible supply, and it is g'ener- 

 ally so distributed that it can be obtained for use on existing roads at small 

 cost. 



Occasionally the discovery of bodies of magnetite ore in the green- 

 stones is announced. The greenstone contains large quantities of magnetite 

 as an essential constituent. This occurs, however, disseminated through 

 the rock in very small particles, which make up an exceedmgly small 

 percentage of the total mass. While the occurrence of the ore bodies 

 reported has in no case been verified, it would not be at all surprising should 

 iron-oxide bodies, of very limited extent, however, really be found. The 

 explanation of their occurrence would be similar to that of the occurrence of 

 almost identical iron-oxide masses in the gabbro ; that is, they are the result 

 of processes of segregation from the basic magma. It is not believed, how- 

 ever, that any such bodies that may be found would prove to be of commer- 

 cial value. The iron oxide occurring in minute quantities scattered through 

 the greenstone contains titanium — it is a titaniferous magnetite — and the 

 probability is that any ore bodies found in this greenstone would likewise 

 consist of titaniferous magnetite They would then correspoiid in their 

 chemical composition, as well as in their mode of origin, to the ore bodies in 

 the gabbro. Moreover, since the processes of liquation and fractional crys- 

 tallization, as the result of which such bodies are formed, would be most 

 fully carried out in those cases where the rocks remain under essentially 

 the same conditions of temperature and pressure for a great length of time, 

 we should naturally expect to find the largest bodies of oxide in the coarsest- 

 grained rocks. Hence, continuing the comparison of the bodies of ore 



