Prof. Le Conte says: “There are in many parts of California two systems of river beds--an old and a new.... The old, or dead, river system runs across the present drainage system in a direction far more southerly; this is especially true of northern members of the system. Farther south the two systems are more nearly parallel, showing less movement in that region. These old river beds are filled with drift gravel, and often covered with lava.” The lava referred to is relatively of modern origin, and the molten streams have in many instances covered the ancient streams, and in others cut them in twain. The “Blue Lead” is a very old river bed that has been the principal source of supply of the placer gold of the northern mines, and it must have existed as a river long anterior to the more modern upheavals that disturbed its course by forming mountain torrents to rend its barriers and cut across its channel. That channel crosses some of the present tributaries of the Sacramento and San Joaquin and contains fossil remains of trees, plants and fruits not now indigenous to California. The well rounded boulders and pebbles found in the beds of these ancient rivers render it probable that they were of considerable length, and that they may have been the channels of very ancient glaciers. It is also probable that the region covered by glaciers at different epochs is much more extensive than has been generally supposed. To me it appears probable, that during some of the eras of formation, they may have stretched across the entire continent. I have not space to give in detail the evidences of glacial action, but will simply state that _remains_ of glaciers may be seen by an observing eye at intervals from the Atlantic to the Pacific; in Minnesota and in the Rocky Mountains, they are especially abundant. Prof. Le Conte says: “The region now occupied by the Sierra range was a marginal sea bottom, receiving abundant sediments from a continent to the east. At the end of the Jurassic, this line of enormously thick off-shore deposits yielded to horizontal thrust, was crushed together and swollen up into the Sierra range. All the ridges, peaks and canyons, all that constitutes the grand scenery of these mountains are the result of an almost inconceivable subsequent erosion.”