70 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
origin, and evidently entertained views quite similar to those of Mr. W. P. 
Blake, supposing the erosion of the gravel deposits, which he calls “ shingle 
terraces,” to have taken place during the upheaval of the continent.* 
In 1860, M. Laur, Ingénieur au Corps Impérial des Mines, was sent by the 
French government to California and Nevada, for the purpose of examining 
and reporting on the gold and silver mining interest of those States. In the 
course of his investigations, he spent two months among the hydraulic and 
quartz mines of the Sierra Nevada, and published his account of them in 1862 
in the form of a Report to the Minister of Public Works. M. Laur describes 
the high gravel deposits under the designation of “auriferous alluvia posterior 
in age to the basalt.” He considered them to have once extended over the 
whole western slope of the Sierra, and maintained that they were thrown 
into confusion (bouleversés) by the phenomena attendant on the eruption of 
the basalts.| The views of this mining engineer were extremely crude; he 
seems to have entirely misapprehended the nature of the phenomena and to 
have failed to notice some of the most striking facts connected with the 
occurrence of the gravel deposits, — facts which, even at that early period, 
had made a strong impression on the miners themselves. 
During the years previous to 1860 there seem to have been many articles 
published in the Californian newspapers in regard to the real nature of the 
high gravels. Few of these can now be obtained, and most of them have 
never met the eye of the writer. Some extracts, however, are preserved in 
Mr. J. S. Hittell’s Mining in the Pacific States of North America. In an 
have respecting the age of the terrace-accumulations is very imperfect. There can be no doubt that those 
occupying the valleys of the Rocky Mountains, being farthest from the coast and at the greatest elevation, 
are the most ancient, and that from the time of their deposit till now the rearrangement of the same ma- 
terials has been carried on during the gradual uprising of the continent.” — James Hector, M. D., in 
Quarterly Journal of the Geological Society of London, Vol. XVII. 1861. pp. 404, 405. 
* “Tt must have been during the period when this denudation of the eastern plains accompanied the 
gradual emergence of the continent, but acting with very different results on the rocky sea-bottom and 
successive ranges of iron-bound coast presented by the western slope, that these immense deposits of 
shingle were formed and moulded into terraces.” — Hector, l. ¢. p. 405. 
t+ “ Les alluvions auriféres de formation antérieure au basalte constituent par leur étendue et leur épais- 
seur les mines d’or les plus importantes de Californie. .... Cette formation s’étendit primitivement 
sur tout le versant occidental de la Névada; elle fut ensuite bouleversée par des phénomenes de ]’époque 
des basaltes. En certains points, les dépots furent recouverts par des coulées basaltiques ou des couches 
de tufs sous lesquelles ils sont aujourd’hui exploités. Ailleurs ils furent attaqués par de violentes érosions 
qui les firent disparaitre sur tout ou partie de leur épaisseur.” — P. Laur, in De la Production des Métaux 
Precieux en Californie. Rapport a s. Exc. M. le Ministre des Travaux Publics. Paris, 1862. 
