CLASSIFICATION OF "'HE DEPOSITS OF AURIFEROUS DRIFT. 277 
remains; but at other points they are found in extensive plateaux or gently sloping table- 
lands bordering the rivers, which have cut their way downwards through the strata and exposed 
them to view. The table-like hills or mountains seen from Knight’s Ferry, on the Stanislaus, 
and between the Mammoth Grove and the Great Cave, are examples of these deposits. In many 
places they are overlaid by a stratum of basaltic lava, like that at Fort Miller, on the San 
Joaquin. It is most probable that the principal deposits of this great series of nearly horizontal 
strata, flanking the Sierra Nevada in the Gold Region, are of the same age as those from which 
fossils were obtained further south along the Tulare valley. Marine Tertiary fossils are 
abundant at Chico Creek, and at other places along the eastern side of the Sacramento Valley. 
Indications of the Cretaceous rocks are also found. 
The overflows of basaltic lava constitute an important feature in the geology of the Gold 
Region. They are found to overlie the auriferous drift as well as the older strata, and produce 
the remarkable flat-topped hills called Table Mountains. 
There are many varieties or modifications of the auriferous drift, or, we may say, of the 
deposits of gold. We find: 
First. A coarse, boulder-like drift, the result of great abrasion and powerful currents in a 
great body of water. i 
Second. A river-drift, or coarse alluvium, ancient and modern. 
Third, Alluvial deposits on flats and over broad surfaces, not confined to river channels. 
: Fourth. Lacustrine deposits—at the bottoms of former ponds or lakes. 
The deposits of the first class are very irregular, and differ in their lithological characters 
and manner of deposition at different localities. The observations were sufficient to show that, 
in many cases at least, the accumulations are extremely local, and that they were not trans- 
ported from a great distance. The great deposit of quartz boulders, and sand of the same 
material, at Michigan City, is regarded as an evidence of the comparatively local character of the 
force, or current, which deposited them ; for ifit had been extensive, or had flowed in a similar 
manner for a great distance, other rocks and gravel would have been mingled with the drift. 
At Forest Hill, also, the gold is found in crystals, but little water-worn or rounded; and quartz 
crystals are taken out with the crystalline planes scarcely scratched, but with their angles 
broken off, so that the effect of a current is shown. Deposits of this class contain coarse lumps 
and grains of gold, and are found on the high table-lands, or ‘‘divides,’’ between the rivers, 
often at an elevation of over 2,500 feet above them. 
The river-drift containing gold, appears under a variety of forms. It may be either coarse or 
fine ; but is found of all ages, from the accumulations now forming in the beds of the streams, 
and in bars, to the deposits of rivers which formerly flowed over the surface 2,500 feet higher 
than now. The courses of such ancient streams are discovered by the miners, and followed by 
them in their underground explorations. All the peculiarities which the beds of rivers present— 
the water worn surfaces, pot-holes, and fine scale gold—are found in them. : 
The rich deposits of gold found in the thin layer of gravel and clay, spread over broad areas 
or “flats,” are mentioned as forming a third class. "They differ from the linear deposits formed 
by Streams, and yet they appear.to be the result of a continuous current passing over the sur- 
face. In many instances such deposits give evidence of having existed as a marsh or swamp, 
or as a low district, inundated at times by rivers, and serving as a repository for a portion ot 
their suspended alluvium. In many of these deposits, however, the masses of gold are quite 
avy, and the grains as coarse as those in the first class of deposits. It is probable that the 
