198 Siluria. [April, 
are of the same age. These facts have an important bearing on the 
question of our future coal-supply, and are, therefore, more especially 
worthy of record. 
More than twenty years ago Sir Roderick Murchison made a 
great stride in advance of other geologists by showing that in 
certain cases the mineral riches of distant lands may be predicted 
by means of geological data. In the year 1844, having recently 
returned from the auriferous Ural Mountains, he examined a col- 
lection of rocks from Australia, and from their similarity with those 
occurring in the Russian range he expressed his surprise that “no 
gold had yet been detected” in the Australian “ Cordillera.” The 
fact that gold had been detected (the discovery being then unknown 
in Europe), is the strongest possible proof of Sir Roderick’s induc- 
tion being, in a scientific sense, a real discovery ; while the memoirs 
which he published on the subject in the years 1844-6 testify that 
his comparison of the two regions was not a ere haphazard surmise, 
but the result of a scientific comparison of the rocks, and the 
earnest belief of a geologist in the method and principles of his 
science. The principles as to the distribution of gold in the earth’s 
crust, upon which Sir Roderick then relied, have since undergone 
some alteration, but only to show that gold is somewhat more 
widely distributed than was at that time supposed. In place of 
the Lower Silurian deposits being the only matrix in which gold is 
found an situ, which was Sir Roderick’s original induction, we now 
know that they are but the chief depositories of the precious metal. 
No one, however, acknowledges this extension of our knowledge of 
the possible sources of gold more freely than the author of ‘ Siluria ; 
and as the subject is one of great economic importance, we quote, 7 
eatenso, his most recent conclusions (p. 472) :— 
1. That looking to the world at large, the auriferous vemstones 
in the Lower Silurian rocks contain the greatest quantity of gold. 
2. That where certain igneous eruptions penetrated the Secondary 
deposits, the latter have been rendered auriferous for a limited 
distance only beyond the junction of the two rocks. 
3. That the general axiom before insisted upon remains, that all 
Secondary and Tertiary deposits (except the auriferous detritus in 
the latter) not so specially affected never contain gold. 
4, That as no unaltered purely aqueous sediment ever contains 
gold, the argument in favour of the igneous origin of that metal is 
prodigiously strengthened; or, in other words, that the granites 
and diorites have been the chief gold-producers, and that the 
auriferous quartz-bands in the Paleozoic rocks are also the result 
of heat and chemical agency. 
Some other additions to our knowledge of the geological struc- 
ture of the British Isles have a purely scientific value. Such, for 
instance, are the determination of the Lower Llandeilo age of the 
