'68 BULLETIN OF THE 



except the lamination plane, can be shown more easily than in the for- 

 mer case. 



The ore and jasper seem to have been erupted in huge bosses and 

 overflows, as well as intruded into the schist in the form of long arm- 

 and wedge-like masses or sheets. On account of the banded character 

 of the jasper, and the intrusion generally being nearly in line of the lami- 

 nation in the large mass, they have an apparently stratified character 

 to those who believe any " striped" rock is a sedimentary one; but when 

 examined in detail, and in places where the relations can be seen, they 

 prove to be eruptive. Those who advocate the sedimentary origin only, 

 take the jasper and ore as a whole, and, because it is apparently to them 

 stratified, assume without further question or examination that it is so. 

 We have gone upon the principle, that the relations of rocks to one an- 

 other show the origin of each one except the oldest, and this must be 

 the arbiter in every case when the other characters are doubtful or are 

 questioned. It happens then that this is largely a question of methods 

 and principles of observation. 



The natural work of mining is to obscure or destroy the geological 

 evidences; furthermore, the natural changes that have taken place in 

 the constitution of the rocks, the decomposition, the uplifts, fractures, 

 foldings, and other accidents which they all have suffered, tend to in- 

 crease the difficulty of finding such proof. Of necessity the characters 

 show best upon the walls of abandoned open pits which the rain liad 

 washed clean, but they were also found in the present workings. Like- 

 wise they are best studied in comparative!}' small masses, partly because 

 their relations are easier seen, and partly because the miner generally 

 leaves no others that can be studied. We were enabled, however, to 

 observe the intrusive relations, not only of small masses, but of some 

 containing thousands of tons. The small masses were, however, either 

 seen to be joined, or had been joined until cut off by mining, to the main 

 body. The view that they have been rendered plastic in situ is not sus- 

 tained by the facts, and when we take into consideration the associated 

 rocks is absurd on its face. The facts, then, sustain the views and ob- 

 servations of Messi'S. Foster and Whitney, and show that the work of 

 the other observers * has been superficial and inaccurate. We are 

 well aware that objections from a metallurgical or chemical stand- 

 point have been raised against the theory of the eruptive origin of 

 hematite and silica together, in such forms as we now find them. If the 

 ore was magnetic at the time of eruption, and has since been altered, 

 this objection is then done away with. The secondary changes that 



