On the California Gold Region. 151 
place if we use a concave lens, or if we turn the refracting 
angles of the two prisms inwards. 
Hence, it follows, and experiment confirms the inference, 
that we give solidity and relief to plane figures by a suitable 
application of colour to parts that are placed at different dis- 
tances from the eye. 
These effects are greatly increased by using lenses of 
highly-dispersing flint glass, oil of cassia, and other fluids, 
and avoiding the use of compound colours in the objects 
placed in the stereoscope. 
On the California Gold Region. By Rev. G. S. LyMAN.* 
From the western base to the summit of the range of the 
Sierra Nevada, is a distance generally of a hundred miles, or 
more. ‘The western slope is broken and precipitous, and 
through the deep ravines that abound, flow the numerous 
mountain-streams that form the tributaries of the Sacramento 
and San Joaquin rivers. The gold region is a longitudinal 
strip or tract, from ten to forty miles in width, lying about 
midway, or a little lower, between the base and summit of 
the range, and extending in length a distance of many hun- 
dred miles; active operations being already carried on through 
an extent of four or five hundred miles at least. The gold 
mines near San Fernando in a spur of the same range, and 
which have been known and worked to some extent for many 
years, are doubtless a part of the same great deposit. 
On approaching the gold region from the valley of the 
Sacramento or San Joaquin, soon after leaving the plain, the 
attention is arrested by immense quantities of quartz peb- 
bles, slightly rounded, and of the size of walnuts, scattered 
over the gentle elevations which form the western base of 
the Snowy Mountains.+ There is here but little soil; the 
earth is of a yellowish-red colour, and nearly destitute of 
vegetation. Nearer to the gold deposits the quartz pebbles 
* In a letter to one of the Editors of the American Journal of Sciences and 
Arts, vol. viii., No. 24, Second Series, p. 415. 
+ See Observations by J. Dana (2), vii., 257, 261. 
