166 KANSAS CITY REVIEW OF SCIENCE, 
superficial deposits of gold are for the most part confined to the foot-hills of 
mountain ranges, and are the products of the erosion effected by ages of frost, 
sun, rain and ice, which are continually wearing down all the more elevated por- 
tions of the earth’s surface. Shore-waves also, in some instances, have worn 
away the rocks against which they have beaten, and have produced accumulations 
of debris that contain gold, platinum, gems, etc., in sufficient quantity to be 
economically worked. When a beach deposit of this kind has been raised above 
the sea-level, it sometimes becomes convenient and profitable mining ground. 
On the coast of Oregon, at and above Port Orford, the beaches now yield gold, 
iridium and osmium in sufficient quantity to afford profitable employment to 
quite a mining population; and in the Black Hills, the old Potsdam sandstone 
beach, formed by the beating of the Silurian sea upon cliffs of Laurentian and - 
Huronian rocks traversed by auriferous quartz-veins, now constitutes what is. 
there known as the ‘‘cement deposits,” from which a considerable portion of the 
gold of this region is obtained. As has been mentioned, however, the chief 
supply of gold in all ages has come from the debris that have accumulated at the 
foot of mountain slopes. All mountain chains are composed of metamorphic 
rocks, and nearly all the mountain ranges of the globe are traversed by quartz- 
veins, in which are concentrated much of the gold that was originally finely 
disseminated through the sedimentary strata—conglomerates, sandstones, shales, 
etc.—now granites, schists and slates. 
By the lateral pressure that has metamorphosed the sedimentary rocks, 
and produces the segregation of the quartz-veins, great folds and ridges were 
formed, which, rising high above the general surface, act as condensers of mois- 
ture and receive the most copious precipitation from the clouds. Hence on 
these mountain sides an enormous system of water-power is developed, which is 
spent in grinding up the rocks and transporting the dedris to the bottom of the 
slope. Here it is further washed, stored, and the gold locally concentrated to 
form the rich ‘‘ placer” diggings. As no great skill or expensive mining machin- 
ery is required to work placer deposits, every man with good health, a pick, 
shovel, pan and stock of provisions may go into the business. Gold washing is 
the simplest, as it was probably the earliest, of all mining enterprises, and has 
at different times employed nearly the entire population of a district or country. 
It is not surprising, therefore, that it has resulted in the production of an enor- 
mous quantity of gold. It is evident, however, that most of the placers of the 
world have been already exhausted, and while the little-known continent of 
Africa promises to furnish a large amount of the precious metal from its ‘‘golden 
sands,” we can hardly expect that the production of California, Australia and 
New Zealand will ever be repeated in the world’s history. 
STRATIFIED DEPOSITS. 
These may be subdivided into several groups, such as: 
1. Ore forming entire strata; for example beds of iron ore. 
