208 Reviews— Silliman’s American Journal. 
have been further degraded, and hollowed into new valleys; but, 
protected by their covering of hard flat lavas, these gold-bearing 
gravels, once lying lower than the surface of the channelled moun- 
tain-sides, have been left, to form ‘high plateaux between the present 
river-canons, and flat-topped ridges known as ‘“ Table-mountains,” 
hundreds, or even thousands, of feet above the present river-beds. 
Thus the topography of the country is exactly the reverse of what 
it was at- the commencement of the present geological epoch: what 
were once valleys are now ridges, and the ridges of former times 
were where the immense cafions of the rivers flowing down the 
western slope of the Sierra now are.’ 
Tunnel- and placer-diggings for gold are carried on both in the 
Pliocene deposits just mentioned, and in the later or Post-tertiary 
gravel-beds formed since that period of greatest voleanic activity 
alluded to above. The latter belong to the epoch of Man; for it 
appears ‘that the Mastodon and Elephant, whose remains are so 
widely and abundantly scattered through California, have been 
contemporaneous with Man in that region.’ 
Notices of new facts and views in Chemistry, Physics, Mineralogy, 
and Geology, and other miscellaneous matter, complete the Number. 
No. 114, for November, contains an elaborate paper On the Origin 
of the Prairies of the Valley of the Mississippt, by Prof. A. Winchell, 
who considers—1. That the soil of the Prairies is of lacustrine forma- 
tion. 2. That lacustrine sediments inclose but few living germs. 
3. That the ‘diluvial’ deposits, on the contrary, are found every- 
where replete with living germs. ‘That the ‘diluvial’ deposits were 
buried during the glacial epoch. 5. That in proportion as the 
‘diluvial’ surface become exposed, the flora of the pre-glacial epoch 
was reproduced. 6. That the vegetation which finally appeared on 
the drained lacustrine area was extra-limital, and was more likely 
to be herbaceous than arboreal. Many facts are well grouped to- 
gether in this paper; and though we do not agree with the author 
as to the dearth of seeds in lake-mud, nor as to the long-continued 
vitality of buried seed, yet, in connection with this interesting subject, 
may be cited the opinion, which some cryptogamic botanists now hold, 
that the Arctic and Sub-Arctic forms of lichens and mosses, which 
have been noticed growing upon the ice-carried boulders in Suther- 
land- and Ross-shire, occupy the life-bearing surfaces of eryptoga- 
mous vegetative patches which existed upon the rock before it was 
drifted southward, into a warmer and more genial clime. Having 
noticed, during a late visit to the North Highlands, several such 
boulders, bearing lichens, of species having for a natural habitat a zone 
very far north of the spot they now rest in, Mr. G. E. Ropgrts, F.G.S., 
has called attention to the subject in a letter, entitled ‘ Boulder Flora,’ 
to the Editor of ‘John o’Groat’s Journal.’ He has suggested therein 
that some curious results may reward the labours of those botanists 
* The gold-bearing shingles of California, and the hydraulic works, are described 
also ay Dr. Hector in the Quart. Journ. Geol. Soe., vol. vii. p. 404; and those of 
Peru by D. Forbes, at p. 20 of the same volume. 
