United States Congressional Serial Set Volume 11716 (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: ceous rocks of the Rampart region and that there is no proof that the granites of the upper Copper basin are later than up]er Carboniferous. It is ]erhaps fair to assume that there was a general period of intrusion, beginning, possibly, in late Paleozoic time and in some parts of the province extending through to the I'pper Cretaceous but having its maximum development late in the Jurassic period. There are many dikes of various types of intrusive rocks, however, which cut the two schist series yet which have been deformed and metamorphosed with them. These dikes, therefore, are younger than the schists but older than the granitic masses, which are little or not at all metamorphosed. MINERAL RESOURCES. GOLD PLACERS. GENERAL DESCRIPTION. The localities in which placer gold in paying quantities has been found in this region all lie in the foothill belt between the Tanana Flats and the high schist range to the south. (See PI. IT, in pocket.) Furthermore, the placers all occur in the valleys of the smaller streams which were either north of the area invaded by ice at the time of the maximum glaciation or were themselves not occupied by glaciers. It may be that formerly there was a concentration of gold in the valleys of the main range, but if so this gold was removed by the ice and scattered throughout the moraine deposits, and postglacial erosion has been insufficient to reconcentrate it or to form .new placers. Colors can be found in almost all the streams of (he foothills, but gold in paying quantities has so far not leen found talween Little Delta and Delta rivers. The streams between Wood and Xenana rivers are peculiar in that in their northward courses from the high mountains to Ihe Tanann Flats they cross one or two, one of them four, hard-rock ridges into which th...