REVIEWS. 
459 
number of the "SidurdiiY Review" are so inueh to the purpose, that we cannot 
better ex])ress our own opinion tlian liy (pioting them. 
"Liebig justly notices the excessive dilHeully of really good observation. It 
is an art Only aequin^d by h)ng ])racticc and culture. I'eoijlc s])eak of facts 
with a coulidence which, to the pliilosophcr, is ciuite amusiug. lie is as ready 
as they can be, (;ven more so, to admit the validity of facts ; but he is not so 
r(!ady "to a(hnit that Wic observations they christen by that name are true facts. 
'The man,' says Liebi^, 'who only sees with his eyes an o))jcct before him has 
no claim to the title ot an observer, which is reserved for him who takers notice 
of t he diU'crent jjarts of the object, and sees the connect ion bet ween the ])arls 
and the whole.' There are 'facts' to supjiort every absurdity. No specvdation 
was ever so baseless as not to have some 'facts' on which to rest. But 'uuuiy 
individuals overlook the half of an event through carelessness ; another adds to 
wliat he ol)servcs the creation of his own imagination ; wliilst a tliii'd, who sees 
sufficiently distinctly the cbifercnt i)arts of the whole, confo\mds together things 
which oug'ht to be kept separate.' " 
lleturmng now to Captain Thomas's pampldet. On the whole we are ex- 
tremely disappointed with it ; and that at tlie end of fifty years' experience a 
naturally intelligent man has so little to eonunuuieate is the severest connnen- 
tary on the whole system of which he is a representative. He of coia-sc tilts 
against the doctrine of the igneous origin of granite, elvan, and trap. Speakmg 
of the former, to which he also refers as " primitive," " innnoved," he says : 
" The ideas suggested by its structure, as well as by the lofty hiUs and unbroken 
plains formed out of it, are those of substantiality, fii'muess, immovability, just 
such as we luight expect it to be coming fresh from the hands of its Creator ; 
exhibiting in the mass no signs of distui-l)ance by the elements, no rcncbng, or 
upheavals by earthquakes, &c." And this, our readers nmst 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 ns see what Captain Thomas lias 
to say on the subject of metalliferous vems. One of his best jjoints — indeed, 
the only one worthy of much notice — is the distinction which he very forcibly 
draws between the different structural characteristics of the Cornisli granite, 
and their bearing on the productiveness of the lodes. He classes this rock, as 
7)/-w;i7iyc and ^tfco/irfary, which he thus defines, with their effects on metalliferous 
production. We quote at some length, because the point is an important one, 
and eamiot be too clearly understood. 
" Hitherto no profitable mine has l)een found for tui, lead, or copper in what 
I beg leave to distiuguish by the term primili.re (jranite. It is hard and com- 
pact, and may generally be cleaved in straight lines as we see it used for build- 
nig-purposes. It is found in most of our high hills with j)rojeeting tops. It 
is commonly found, too, in the central parts of granite districts, even where 
there are no projecting tops, at no great dei)th below the surface. 
" At the sides and flat bases of such lulls, as well as in the hollows between 
high hills and the margins of granite districts, anotlier 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 irregular ; very jointy ; frequently 
containing hornblende and chlorite ; is traversed by regularly fonned elvan- 
courscs, 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 hUls ; the base of lofty peaks rising from 
the interior of such districts, and sometimes rising in such situations into small 
liiUs itself. ... A narrow margin only of some granite districts is of this 
kind, although a thin layer of it sometimes overspreads pretty large portions 
