362 REPORT— 1869. 



tional cases ; the great majority of the open fissures are beyond and without 

 this influence, and it must be obviously impossible, to any great extent, 

 where the fissures have been refilled, that there could be the passage of any 

 considerable bodies of water through them since they have obtained their 

 present elevations, in some instances amounting to several thousand feet 

 above the sea-level. It appears to me, therefore, more probable that the de- 

 nudation to which they have been subject is due in great measure to the long- 

 continued action of marine cm-rents, whilst the fissures, the upper jjarts of 

 which afford the most striking evidence of this condition, still remained 

 open beneath the sui'face of the ocean. This might have been for greatly 

 extended periods, as there is evidence throughout the Mendip and South 

 Wales districts that the Carboniferous Limestones formed the floor of the 

 sea through Triassic, Liassic, and Oolitic times. 



After the disturbing influence by which the fissures were caused, their 

 filling up by derived materials, and the time occupied thereby, must have 

 depended upon local causes that were in operation in the several areas in 

 which they occurred. In some instances, where little or no sedimentary 

 matter was being derived from adjoining lands, or where no preexisting 

 stratified deposits were being denuded, few materials for this purpose would 

 be supplied, and a greater length of time would elapse before the fissures re- 

 ceived their vein-stuff', of whatever kind, whilst ou the contrary they would 

 more or less speedily have received the deposits with which they are now 

 filled, subject, in either case probably, to a scouring out and occasional mo- 

 dification of the material within their walls. 



Contents of Fissures. — In working for various minerals, it is usually found 

 that the more precious contents of the veins are either in vertical strings, in 

 bunches or pockets, or more rarely in flats, and that they form but a very 

 small part of the contents of the fissures. When attention is given to the 

 other materials which form by far the greater bulk of the infUhng, it wiU be 

 found in some instances to be of a very varied character, those even in 

 the same mine being most remarkable. Though in general there might be an 

 agreement in the character of the deposit in the same mineral field or area, 

 when separate districts are examined, the distinction is more marked ; often 

 the material brought into the vein is conglomeratic, consisting of both angular 

 and rolled pebbles — in the former case probably derived from the adjacent 

 walls of the vein, or from a source not far removed ; in the latter case, which 

 is not an unfrequent one, the pebbles are from rocks not contemporaneous, 

 some of which have therefore a foreign origin, and, either in being brought 

 from a distance or from the subsequent action of the water in the fissure, ■ 

 have been as much rounded as are some of those found in the drifts of our 

 superficial quaternary deposits. The cavernous interstices left in such con- 

 glomerates are favourable to the deposition of minerals for which the veins 

 are worked ; and where this is not the case, they are usually cemented to- 

 gether by carbonate of lime, quai-tz, or some other material incident to the 

 infilhng. 



Still more frequently, in many districts, from forming the great bulk of 

 the infilling, the "dowky" portions, or the clays, of the veins are chai'gcd 

 with varying deposits of a sandy nature, with marl or clay, or with a me- 

 terial assuming a variegated or finely conglomeratic character, showing an 

 admixture brought from diff'erent sources, or by the denudation of beds of 

 different mineralogical conditions, analogous to stratified deposits when 

 brought together by opposing currents. The variety in the character of the 

 vein-stuff is at times most marked; and there may be obtained from the 



