ON MINERAL VEINS IN CARBONIFEROUS LIMESTONE. 365 



shells and plants abundantly. Of this, through a long examination of the 

 contents of mineral veins, I have seen no evidence either in the Alston or 

 any other mining-district. 



Postpliocene caverns and fissures have, however, remained open to this 

 time, in many instances, in our Carboniferous-limestone ranges ; and although 

 they have been within the influence of, and subject to, the effect suggested by 

 Mr. Wallace, their organic contents consist chiefly of the extinct mammaUa 

 of that period, whUst their mineral deposits are confined to the stalactitic 

 and stalagmitic deposits on their roofs and floors which have been slowly 

 accumulating since the postpliocene period. 



The Neptunian theory, fh-st advanced by Werner for the origin of mine- 

 rals, would probably before this have received greater attention but for the 

 other extravagant ideas he connected with it. I shall now offer some sug- 

 gestions regarding its probable truth. 



It appears to me necessary, in the first place, that, for the production of 

 minerals, there should be the following elements or conditions, viz. the pre- 

 sence of the minerals themselves in the waters of the ocean, open fissures 

 communicating therewith, favourable electrical conditions, and time for 

 their precipitation. 



It has now been established, without doubt, by the highest chemical 

 authorities, that many of our most important minerals are present in minute 

 quantities in the waters of the ocean. This is admitted by those who be- 

 lieve in segregation, the difference being that they think it was first de- 

 posited and afterwards extracted from the parent rock, and redeposited in 

 the veins, rather than originally collected in the veins themselves. 



As regards the connexion subsisting between the ocean and the vein- 

 fissures, I beheve it wiU be recognized to be the case that, in the great 

 majority of instances, the different veins come directly to the surface, and 

 wherever a later rock has been deposited, which is only in exceptional cases, 

 covering up the mouth of the vein, there will stiU be found a break in the 

 sequence of the strata, which might give almost unlimited time for the pre- 

 cipitation of the minerals therein. "WTierever systems of veins occur, it is 

 probable there wiU be found connected there-nith an abnormal condition 

 and considerable breaks in the deposition of the rocks. I have shown this 

 to be the case in connexion with the Carboniferous Limestone of the Mendip 

 range, and its continuation through South Wales, in which districts it can 

 be seen that those rocks were, through enormous periods, exposed to the 

 influence of the ocean, possibly forming reef-like barriers around the edges 

 of the carboniferous basin, the fissured veins and floor of this sea-bottom 

 receiving at some periods materials of Ehaetic or of Lower or Middle Lias 

 age, whilst an occasional capping of the beds of Inferior Oolite, left in some 

 Carboniferous Limestone trough, now and then cover up the mouths of the 

 veins that had received aU their contents prior to its deposition. Some 

 most instructive examples are present in this district, in which it may be 

 seen that whilst there are on the walls of the vein the usual vertical con- 

 ditions of vein-stuff, such as calespar, suljAate of barytes, &c., with occa- 

 sional haematite iron-ore, calamine, and galena, the central portion of the 

 vein is unmistakably of Liassic or Rhsetic age. In all such instances there 

 are combined the elements of open fissures communicating with the ocean, 

 and greater or less time in the reception of their contents. 



Various Ages of Minerals. — It wiU be found that minerals generally occur 

 in the oiitcrops of lines of strata, possibly occupying, to some extent, the 

 same relative positions, as regards the strata by which they are now sur- 



