1869.J MACFARLANE — GEOLOGY OP LAKE SUPERIOR. 45 



crosses the general course of the dykes, aud it is to this class that 

 the vein belongs in which silver, to a considerable extent, was 

 discovered. 



This vein occurs en a small island, marked Silver Islet on the 

 map, and distant about a mile from the main store. This islet 

 (No. 4), the reef and larger island (No. 5) to the eastward, and 

 the still larger isiand to the south-westward, marked Pyritic 

 Island, appear to be all that remains of a large dyke or mass of 

 diorite, which in all likelihood intersected the sedimentary strata 

 which, in former times, occupijd the space between the islet and 

 the mainland. The width cf this intrusion of diorite is at least 

 100 feet, but may be more in depth, as a good part of its thick- 

 ness must have been worn away by the action of the waves of the 

 lake. The nature of the rock of the islet has been ah-eady 

 described. It differs from most of the rocks of the other dykes, 

 not only mineralogically, but, also, in being destitute of the 

 divisional jointing which so frequently characterizes them. A few 

 square yards only of the islet, at its highest part, six feet above 

 the level of the lake, shew any traces of vegetation. The 

 remainder has been smoothed and rounded off by the action of the 

 water, and here the rock seems exceedingly compact, no fissures 

 being perceived. On the map will be found a plan, on a larger 

 scale, of this islet, shewing the position and course of the vein 

 which traverses it. The course of the vein is N. 32° to 35° W., 

 and it dips to the eastward at an angle of about 80°. It has a 

 width of about twenty feet on the north side of the island, and to 

 the southward divides into two branches, each seven to eight feet 

 wide. It consists mainly of calcspar and quartz. Galena, in 

 little cubes, is visible in almost every part of it, and blende, iron 

 and copper pyrites are not uncommon. The native silver, accom- 

 panied by silver glance, was only found in the west branch. It 

 was first noticed by Mr. John Morgan, one of the exploring party, 

 in the shape of small nuggets, on the east side of the vein. It was 

 then traced to the water's edge, and out into the water for some 

 distance, where, instead of merely scattered nuggets of native 

 silver, large patches of veinstone, rich in galena, are visible, which 

 galena, on closer examination, is found to be intermixed with 

 small particles, and some large nuggets of silver. The thickness 

 of the rich part of the voin varies from a few inches to two feet, and 

 it keeps to the east or hanging side of the vein. By working in 

 the water with crow-bars, some loose pieces of rich veinstone were 



