1864.] Geology and Palcontology. 475 
Of the many geological phenomena whose causes are still more or 
less obscure, that of the elevation and depression of portions of the 
earth’s crust is one of the greatest importance, because of its being 
an element of change always present in the mind of the geologist, 
and one of the greatest difficulty because of the protean character 
of the circumstances attending its production, as well as on account 
of the numerous secondary results of which it is the proximate 
cause. 
A new theory of elevation and depression has recently been pro- 
pounded by Professor Bischof (in a second German edition of his 
‘Lehrbuch der chemischen und physikalischen Geologie’), who con- 
siders that all the observed phenomena can be explained by supposing 
them to have resulted from an increase or decrease of volume in 
deeply-seated rocks, in consequence of the more or less complete dis- 
placement of the silica of their silicates by carbonic acid. ‘The 
chemical action and the physical result, which are together believed 
by the author to be the cause of the phenomena in question, may 
conceivably take place in nature, as we know that they can be pro- 
duced by experiment. 
Geologists have long been aware that the greater portion of the 
Scandinavian area has for ages been gradually rising at the rate of a 
few inches in a century, and this circumstance has hitherto baftled the 
ingenuity of every one who has attempted to explain it. But Professor 
Bischof’s statement that the country is undergoing this upheaval only 
in those portions of it where siliceous rocks occur, renders it very 
probable that his theory will apply to a case of this kind, for he would 
scarcely make a statement of such importance had he not ascertained 
the fact to be such as he represents it. In a similar manner he ex- 
plaims the sinking of Greenland, the hydrous silicates which occur 
there undergoing a loss of volume through the displacement of the 
silica by carbonic acid. 
It is, therefore, very probable that Professor Bischof’s theory may 
be found to apply to such cases of gradual upheaval and depression, 
and thus it is surely a great advance in our knowledge of geological 
causes. Had the distinguished author been contented with this limited 
application of his hypothesis, we should not have been disposed to 
cavil at any of his arguments; but when he strives to account for the 
dislocation, contortion, and overturning of strata by merely supposing 
the upheaval to have been of unequal amount in different places, we 
confess that we are more than sceptical. It is easy for a chemist in 
his laboratory to propound such an hypothesis, but it is equally 
easy for a geologist in the field to see that it is very improbable, if 
not impossible. 
Leaving now the region of theory, we may remark that the first 
announcement of a new and startling fact is often a much less impor- 
tant episode in the history of its discovery than the first attempt at 
its confirmation. The case which we are about to notice, namely, the 
discovery of fossils in the Laurentian rocks of Canada, well illus- 
trates this proposition, for when the announcement was first made by 
Sir William Logan, nearly five years ago, at a meeting of the Ameri- 
VOL. I. 2K ; 
