GENERAL REMARKS ON THE TOPOGRAPHY. 111 
connexions." Confusion and error have thus resulted, rendering much study necessary to 
separate the ascertained from the assumed. 
To free the general map as much as possible from this objection, I have, according to my 
instructions, represented on it only such mountains as are known. In some instances where 
the exploration of known ranges was imperfect, they have been but faintly engraved, and the 
word ‘‘unexplored’’ placed near them. This is the case with the Big Horn mountains, the 
Sierra la Plata, and the Blue mountains. In other places, where no explanations have been 
made, spaces are left blank, as in the southern portion of the Great Basin. A serious difficulty 
is experienced in giving a correct graphic representation of level regions furrowed by the 
chasms of large rivers, like the Colorado, because these depressions have, except upon close 
scrutiny, nearly the same effect to the eye as mountain ridges. 
_ The collection of ascertained facts represented on this map far exceeds that of any former 
one of this region. I shall not attempt any description or enumeration of the different parts, 
the map itself being an exhibition, perhaps more full and intelligible than any that could be 
putin words. To prevent the map from exhibiting any bias which my own views may have taken, 
I have copied as nearly as possible the styles of different topographers on the original maps, and 
thus some parts may have peculiarities which belong more to the delineator than to the 
country itself. ۱ 
The publication of the Pacific Railroad maps will probably change some of the former ideas 
of these mountains, and give rise to new speculations as to their directions, equivalents, and 
connexions of different parts. Every one knows how easy it is to generalize ideas where facts 
are few, and in accordance with this, those who have travelled most in the region have 
theorized the least, having seen the immensity of the subject and the difficulties which must 
be overcome to-comprehend it. Those who have investigated merely the travels of others, 
have had only the imperfect representations of the latter on which to theorize. 
It may not be inappropriate here to give some of the general ideas which have successively 
prevailed in regard to these mountains. 
In the earlier periods of North American discovery it was known that there were mountains 
in the interior at its northern and southern parts, and rivers flowing from them to;the two 
great oceans east and west. It was natural to connect these mountains by hypothesis, and to 
consider them as one great chain, separating the sources of these streams. Such an idea 
prevailed at the time of Humboldt’s New Spain. Even now many well informed persons 
consider that a road has but one. mountain summit in n the Mississippi river to the 
Pacific Ocean. : 
When, after the publitatiót of the dicte of Sutter: map makers became aware of the 
extent of the mountains near the Pacific coast, nothing seemed more natural than to suppose 
two great mountain chains—one near the Pacific and one in the interior. If this theory were 
true, we should find a great longitudinal valley between the ranges similar to that separating 
the interior mountains from the Alleghanies, aud we should have but two mountain summits to 
pass between the Mississippi and the Pacific. This idea is practically as erroneous as that of 
one summit, although it still prevails. Such a prominent place did this longitudinal valley 
hold, in the opinions of geographers of earlier times, that we find in Humboldt’s New Spain : 
‘‘M. Malte Brun has started important doubts concerning the identity of the Tacouche Tesse 
and the river Columbia. He even presumes that the former discharges itself into the Gulf of 
California : a bold supposition, which would give the Tacouche Tesse a course of an enormous 
