EE VIEWS. 
355 
Alston Moor. In these lie ararnes, tliat as lead ore is not deposited through- 
out the whole extent of the veins, the}' have not always been filled ith 
minerals or metallic substances; the deposition must therefore be the result 
of certain antecedents ; and he infers that the laws which have regulated the 
distribution of metallic ores may be different from those relating to the 
origination of the metal. Two theories have been proposed to account for 
the origin of ore-veins : the one supposes them to be segregations of me- 
tallic particles from the surrounding rocks, the other regards them as de- 
posits by sublimation from great clepths and connected with volcanic in- 
fluences. It is certain, however, that the laws which have regulated the 
distribution of ore in veins may be of a very different character from those 
connected with its origination ; the former may be mechanical, the latter, 
if metals are substances compounded from certain elements unknown in a 
separate state, must be chemical. If they are simple substances which 
have risen from tlie interior of the earth as gaseous emanations, then the 
accumulation of tlie ore in certain portions of the veins may have taken 
place after its deposition sparsely throughout the whole extent of the frac- 
tures in the rocks ; if the metals are derived from rocks in which their ex- 
istence cannot be detected, then the compounding and localization of the 
ore may have been effected contemporaneously. The experiments of I3cc- 
querel and others have shown that metals in solution may be crystallized 
and combined with other substances by electro-chemical agency, forming 
minerals exactly similar to those found in nature ; but interesting as those 
experiments are, they render no assistance to the practical miner in guiding 
him to the deposits of metallic ores so irregularly distributed in the veins ; 
they relate more to crystallography and mineralogy than to practical 
mining, for cr3"stals of various kinds are found where none of the metals 
exist. No kind of mineral in the veins at Alston Moor varies so much in 
quantity in different parts of tlie same stratum as lead-ore. It is found 
plentifully deposited with quartz, carbonates and sulphides of lime and 
iron, fluorspar, bar^'tes, oxides of iron, black-jack, etc., and it is frequently 
absent in the same stratum when the veins contain large quantities of some 
one or other of these minerals ; hence its deposition is not dependent on 
the presence or absence of any of those minerals, and it is evident that 
whatever caused their deposition has not prevented the operation of those 
causes which regulated the deposit of lead-ore. The variation in amount 
of lead-ore in the same vein and in the same stratum or kind of rock be- 
ing greater than that of any other mineral, the law of such variation is 
more likely to be ascertainable in its case than in any other. In Alston 
Moor the veins have been most productive in situations furthest removed 
from plutonic action ; the richest deposits having been effected in the 
upper part of the mountain limestone, where no igneous rocks are found 
either in the form of dykes, or of sheets intermingled horizontally with the 
stratified rocks. The lower part of the strata in that district includes a 
stratum of basaltic greenstone as well as a basaltic dyke, but the veins 
generally have contained very little lead-ore, where these rocks have formed 
their sides or walls — a circumstance, however, we should think might very 
probably be sometimes due to the sublimation or driving off of the lead by 
the heat of the injected lava in the cases of volcanic dykes. 
So far as the Alston Moor district is concerned, Mr. Wallace thinks 
there is nothing to support the theory that the lead is due to exhalations 
from below, or to matter injected in a fluid state among the consolidated 
sedimentary rocks. The nodules of carbonate of iron, so often found ar- 
ranged in layers of beds of shale, have generally undergone some degree 
of contraction in the interior ; often the exterior has been consolidated to a 
