In Professor Gregory's interesting presidential address contained in your journal for October, there is a reference to the origin of the Sudbury ores, in which he expresses the opinion that they were deposited from solution long after the first consolidation of the rocks with which they are associated. As the Sudbury ore deposits are perhaps the best examples in the world of the magmatic segregation of sulphide ores it seems a pity that the weight of Professor Gregory's authority should be given against the correct view. Probably he has not read the reports on the region by Dr. Barlow and myself in which incontrovertible proof of the magmatic origin of these ores has recently been given. In the report prepared by myself it is shown that all the ore bodies are found at the lower edge of a laccolithic sheet of norite, blending upwards into micropegmatite, or on dike-like projections from this sheet. The laccolithic sheet is 37 miles long, 17 miles wide, and has dozens of ore bodies connected with its basic edge. The adjoining rock may be granite, gneiss, green schists, graywacke, etc., without affecting in any way the monotonous character of the ore. The ore bodies may contain fragments of the adjoining rocks and sometimes also of the norite, for some crushing and faulting has taken place; but everywhere the solid ore passes into pyrrhotitenorite, and then into norite spotted with blebs of ore. The sulphides have sharp boundaries against the adjoining rocks, but blend into the norite.
