We are indebted to the Missouri Advocate for the following account of General Ashley’s discoveries in this quarter. He considers it quite possible to form a route across this formidable barrier to the Pacific Ocean. The route proposed, after leaving St. Louis, and passing generally on the north side of the Missouri river, strikes the river Platte, a short distance above its junction with the Missouri; then pursues the waters of the Platte to their sources, and, in continuation, crosses the head-waters of what General Ashley believes to be the Rio Colorado of the west, and strikes, for the first time, a ridge or single connecting chain of mountains, running from north to south. This however presents no difficulty, as a wide gap is found apparently prepared for the purpose of a passage. After passing this gap, the route proposed falls directly on a river, called by George Ashley the Buenaventura, and runs from that river to the Pacific Ocean. The face of the country, in general, is a continuation of high, rugged, and barren mountains; the summits of which are either timbered with pine, quaking-asp, or cedar; or, in fact, almost entirely destitute of vegetation. Other parts are hilly and undulating; and the valleys and table-lands (except on the borders of water-courses, which are more or less timbered with cotton-wood and willows,) are destitute of wood; but this indispensable article is substituted by an herb, called by the hunters wild sage, which grows from one to five feet high, and is found in great abundance in most parts of the country. The sterility of the country generally is almost incredible. That part of it, however, bounded by the three ranges of mountains, and watered by the sources of the supposed Buenaventura, is less sterile; yet the proportion of arable land, even within those limits, is comparatively small; and no district of the country visited by General Ashley, or of which he obtained satisfactory information, offers inducements to civilized people, sufficient to justify an expectation of permanent settlement. The river visited by General Ashley, and which he believes to be the Rio Colorado of the west, is, at about fifty miles from its most northern source, eighty yards wide. At this point, General Ashley embarked and descended the river, which gradually increased in width to one hundred and eighty yards. In passing through the mountains, the channel is contracted to fifty or sixty yards, and so much obstructed by rocks as to make its descent extremely dangerous, and its ascent impracticable. After descending this river about four hundred miles, General Ashley shaped his course northwardly, and fell upon what he supposed to be the sources of the Buenaventura; he represents those branches as bold streams, from twenty to fifty yards wide, forming a junction a few miles below where he crossed them, and then emptying into a lake (called Grand Lake,) represented by the Indians as being