REVIEWS. 



459 



number of the " Saturday Review" are so mucli to tlie purpose, tliat we cannot 

 better express our own opinion than by quoting them. 



" Liebig justly notices the excessive difficulty of really good observation. It 

 is an art only acquired by long practice and culture. People speak of facts 

 with a confidence which, to the philosopher, is quite amusing. He is as ready 

 as they can be, even more so, to admit the validity of facts ; but he is not so 

 ready to admit that the observations they christen by that name are true facts. 

 'The man,' says Liebig, 'who only sees with his eyes an object before him has 

 no claim to the title of an observer, which is reserved for him who takes notice 

 of the different parts of the object, and sees the connection between the parts 

 and the whole.' There are ' facts' to support every absiu*dity. No speculation 

 was ever so baseless as not to have some ' facts' on which to rest. But ' many 

 individuals overlook the half of an event through carelessness ; another adds to 

 what he obseiwes the creation of his ovm imagination ; whilst a third, who sees 

 sufficiently distinctly the different parts of the whole, confounds together things 

 which ought to be kept separate.' " 



Returning now to Captain Thomas's pamphlet. On the whole we are ex- 

 tremely disappointed with it ; and that at the end of fifty years' experience a 

 naturally intelligent man has so little to communicate is the severest commen- 

 tary on the whole system of which he is a representative. He of course tilts 

 against the doctrine of the igneous origin of granite, elvan, and trap. Speaking 

 of the former, to which he also refers as "primitive," "immoved," he says: 

 " The ideas suggested by its structure, as well as by the lofty hills and unbroken 

 plains formed out of it, are those of substantiahty, firmness, immovability, just 

 such as we might expect it to be coming fresh from tlie hands of its Creator ; 

 exliibiting in the mass no signs of disturbance by the elements, no rending, or 

 upheavals by earthquakes, &c." And this, our readers must remember, of the 

 Cornish granite, which is newer in age than the Carboniferous system, that is 

 broken through by it. 



But leaving aside mere general geology, let us see what Captain Thomas lias 

 to say on the subject of metalliferous veins. One of his best points — indeed, 

 the only one worthy of much notice — is the distinction Avhich he very forcibly 

 di-aws between the different structural characteristics of the Cornish granite, 

 and their bearing on the productiveness of the lodes. He classes this rock as 

 primitive and secondary, which he thus defines, with their effects on metalliferous 

 production. We quote at some length, because the point is an important one, 

 and cannot be too clearly understood. 



" Hitherto no profitable mme has been found for tin, lead, or copper in what 

 I beg leave to distinguish by the term primitive granite. It is hard and com- 

 pact, and may generally be cleaved in straight lines as we see it used for build- 

 ing-purposes. It is found in most of our high hills with projecting tops. It 

 is commonly found, too, in the central parts of granite districts, even where 

 there are no projecting tops, at no great depth below the surface. 



" At the sides and fiat bases of such hills, as well as in the hollows between 

 high hills and the margins of granite districts, another kind of granite is com- 

 monly found, which I distinguish as secondary granite. Although varied in its 

 structure and composition in different localities, the following are some charac- 

 teristic features: fracture rough and irregiilar; very jointy; frequently 

 containing hornblende and chlorite ; is traversed by regularly formed elvan- 

 courses, whilst portions of it, like ribs, project from the main body into the sur- 

 rounding slate. Its localities are some of the outskirts of primitive granite 

 districts ; the hollows between high hills ; the base of lofty peaks rising from 

 the interior of such districts, and sometimes rising in such situations into small 

 hills itself. ... A narrow margin only of some granite districts is of this 

 kind, although a thin layer of it sometimes overspreads pretty large portions 



