REVIEWS 201 



The courses of both vary from northeast to northwest, but there are 

 exceptions to this rule. 



The fissures are not open gaps, as already stated, but are closed 

 lines of fracture along which replacement has occurred. In Dr. Pen- 

 rose's words : " Sometimes there are two or more main parallel cracks or 

 fissures and numerous minor ones, while very commonly the zone of 

 fracturing seems to be represented by no especially well-defined break, 

 but by numerous parallel or approximately parallel cracks, each of 

 about the same magnitude and from a fraction of an inch to several 

 feet apart." . ..." In fact the district may be regarded as an area 

 intersected by numerous zones of fissuring which are separated by an 

 area of less marked but very noticeable fissuring." The ore is found 

 lining both sides of the fissures. 



Faulting is evidenced by grooves and slickensided rock surface. 

 The movements were small in amount, the greatest observed being 

 between twenty and twenty-five feet. 



The minerals of the ore bodies are generally promiscuously 

 arranged, the ore usually being simply the country rock containing 

 greater or less amounts of secondary minerals. Ore is found along 

 some of the fissures or cracks, while others, almost identical in appear- 

 ance, are barren. These fissures are often taken by miners for vein 

 walls beyond which no ore will be found. They hence neglect to 

 cross cut. Dr. Penrose gives a valuable suggestion in advising miners 

 not to be misled by these apparent walls, as valuable deposits will 

 often be found within a short distance beyond them. As an illustration, 

 in a mine operated by the writer about a dozen such fissures, variously 

 mineralized, were encountered in a cross cut of about loo feet. 



A noticeable feature of this camp is that the veins follow the dikes, 

 either in contact, or more commonly in proximity to them. Some- 

 times they cross the dikes and follow them on different sides. The 

 association of dikes and veins is a fact well known by mining men and 

 the presence of a dike, especially of phonolite, causes a claim to be 

 held in much higher estimation. 



In their mode of occurrence the dikes and fissures give evidence 

 of a limited erosion of the district. Thus their upper parts often 

 differ markedly from their deeper parts. " The dip near the surface 

 is frequently at a different angle from that at a depth, and veins which 

 occur in one well-defined fissure at a depth sometimes fork near the 

 surface and appear in separate outcrops. Both these phenomena can 



