We have now traversed the most difficult part of our road. Its Rocky-Mountain section has cost more capital, labor, and engineering skill than all the rest together. The return for this vast expenditure must be no less vast,--but it will be rendered slowly. It does not lie on the surface or just beneath the surface, as in the pastoral and agricultural regions. It is almost entirely mineral, and must be mined by the hardest work. But it ranges through all the metallic wealth of Nature, from gold to iron, and no conceivable stimulus short of a Pacific Railroad could ever have been adequate to bring it forth. We shall find the import trade of Salt Lake by the railroad to consist chiefly of emigrants and their chattels. If Brigham Young be still living, his favorite policy of non-intercourse with the Gentiles may also somewhat diminish the export business of the road. But human nature cannot forever resist the currents of commercial interest; and the Mormon settlements possess so many advantages for the economical production of certain staples, that we need not be surprised to find trains leaving Salt-Lake City with sorghum and cotton for San Francisco, and raw silk for all the markets of the East. From Salt-Lake City to the Humboldt Mountains, we pass between isolated uplifts of trap and granite, over a comparatively level desert of sand and snowy alkali. The terrors of this journey, as performed by horse-carriage, have been fully depicted in our last April number. We may laugh at them now. The question which principally interests us, after we have blunted the first edge of our wonder at the sublime sterility of the Desert, is what conceivable use this waste can be made to subserve. Before the railroad, that question had but a single answer,--the inculcation of contentment, by contrast with the most disagreeable surroundings in which one might anywhere else be placed. Perhaps it is over-sanguine to conceive of a further answer even now. If there be any, it is this: In its crudest state the alkaline earth of the Desert is sufficiently pure to make violent effervesence with acids. No elaborate process is required to turn it into commercial soda and potash. Coal has been already found in Utah. Silex exists abundantly in all the Desert uplifts. Why should not the greatest glass-works in the world be reared along the Desert section of the Pacific Road? and why should not the entire market of the Pacific Coast be supplied with refined alkalies from the same tract? Given the completed railroad, and neither of these projects exceeds commercial possibility.