12 
CONCLUSION OF THE OFFICIAL REVIEW, ETC 
desirable have been made. An analysis of the soil of the alluvial portion of the Colorado 
desert, which covers an area of 4,500 square miles, and is four times greater in extent than the 
land under cultivation on the Mississippi river, between the mouth of Red river and the Balize, 
shows that it has all the elements of great fertility, and, but for the adverse climatic conditions, 
would rival in its productions the best lands of the delta of the Mississippi. According to the 
barometrical levellings of Lieutenant Williamson, the alluvial portion of this plain is lower 
than the surface of the Colorado river ; and should this be confirmed by more accurate modes 
of levelling, as there is every reason to believe it would be, an extensive system of irrigation 
would entirely change the character of its surface by tbe introduction of water, the only element 
required for great productiveness. About one half of the Colorado desert is within our territory. 
Valuable ores of several metals have been brought in and examined, and their localities visited 
and described. A specimen from the collection of Captain Pope proves to be a mass of carbonate 
of lead, nearly pure, and containing seventy-two per cent, of metal. Another specimen of earth, 
from the bed of Delaware creek, contains over eighteen per cent, of free sulphur. In California 
two veins of copper ore, one of iron, and one of antimony, of great extent and richness, have 
been found and reported upon ; worth alone the whole cost of Lieutenant Williamson’s expe¬ 
dition. The character and extent of large deposits of bitumen asphalt near Los Angeles has 
also been made known. The examination of a collection of salty and alkaline incrustations 
from the soil and dry lakes of California, shows that they consist principally of salt, sulphate 
of magnesia, and carbonate of soda. Nitre was not found in any quantity. 
Along the 35th parallel the carboniferous limestone has been found as far west as the San 
Francisco mountain, in longitude 112°. The discovery of these rocks so far west renders it 
possible that deposits of true coal will be found in that region, although, the observations having 
been very limited, none has yet been seen. The probable existence of coal in other new and 
important localities has been indicated, which more thorough examinations may develop. Much 
additional geological exploration is required to throw light on this important subject. 
The character of the sand-hills of the Colorado desert has been carefully considered by Mr. 
Blake, who has shown that they are confined in position to a bank or terrace, and, contrary to 
the opinion previously entertained, do not constitute a formidable obstacle to the construction 
and working of a railroad. 
Among the results of special scientific interest is the determination of the geological age of 
mountain chains. It has been ascertained that the coast mountains, in the vicinity of San 
Francisco, and further south, have upraised within or since the Eocene division of the Tertiary 
period. The strata about San Francisco, Benicia, Monterey, and other localities, have been 
shown to be of Tertiary age, and the foldings and contortions to which they have been subjected 
reveal the violent disturbances and mighty changes of that part of the continent within recent 
geological times. Tertiary marine shells and sharks’ teeth have been brought from the tops 
of hills, at the base of tbe Sierra Nevada, over 1,500 feet above the ocean. 
Of similar interest are the examination and description of volcanoes, the exhibition of the 
nature of the rocks and soils along the several routes, by large collections of rocks, minerals, 
and fossils, and the comparison of the ages of mountains, and the strata on their flanks. These 
additions to our knowledge of the geological structure of the country have been of great assistance 
in determining its general features and topography. 
The results of the investigations into the zoology and botany of the country west of the 
Mississippi have proved interesting and important. The existence and geographical distribution 
