The original Huronian area, as mapped by Logan and his assistant, Murray, lies within the province of Ontario, which contains also its northeastern extension toward lake Temiscaming and several other large and important tracts which have been mapped with more or less certainty as Huronian by Canadian geologists since Logan’s time. As these rocks contain the most promising ore deposits of the province, they naturally attract much attention from prospectors and geologists, and the problems connected with their formation and relationships have an economic as well as a purely scientific interest. The question as to what areas are really Huronian, and as to the relative age of the different areas mapped as Huronian, differing as they often do in striking ways from the rocks of the original region, is one requiring solution if the pre-Cambrian geology of the province is to be placed on an assured basis. During the . . .