on " Researches in Physical Geology" 173 



seems much increased by the fact that partial cavities are fre- 

 quently found in them, more particularly where the vein is 

 very w^ide. Large pipe-veins* are usually filled with sparry 

 substances amongst which the ore is disseminated ; but it fre- 

 quently happens, I believe, that considerable spaces are still 

 left empty, strongly indicating that such was once the case 

 with the whole space occupied by the vein; and it seems 

 highly probable that the usual vertical veins of the district 

 have been filled in the same manner as the pipe-veins, (what- 

 ever that process may have been,) because veins of the former 

 kind always communicate with theselatter (of which the miner 

 considers them i\\e feeders) ; and I am not aware that any cha- 

 racteristic difference has been observed between the substances 

 which occupy these two descriptions of veins. 



Of the formation of the ore of a mineral vein 1 pretend to 

 offer no conjecture. It seems to present an equal chemical 

 difficulty whatever theory we adopt; but that some process 

 of infiltration might be sufficient for the supply of the vein- 

 stuff is indicated, I think, by the great masses of stalactitic 

 formations met with in some cases, and their comparatively 

 rapid formation in others. The toadstone of Derbyshire 

 also contains in many places numerous veins and insulated 

 small globular portions of calcareous matter to the depth of 

 perhaps 200 feet, the formation of which it seems almost im- 

 possible to conceive except by infiltration. To a similar pro- 

 cess too may be ascribed, I conceive, the existence in the in- 

 terior hollows of fossil shells of crystalline substances dif- 

 fering as much from the mass in which the shells are im- 

 bedded, as vein-stuff frequently differs from the containing 

 rock. These and similar facts have appeared to me to prove 

 at least the adequacy of the cause assigned to produce the 

 effects which I am at present disposed to attribute to it. I 

 pretend not to offer an opinion as to whether at some ante- 

 cedent geological period any solvent more powerful than water 

 may have assisted in the })rocess of infiltration. It may, per- 

 haps, not be deemed very impossiblef- 



[To be continued-] 



* Pipe-veins are spaces (frequently of considerable extent) usually existing 

 between the beds of limestone, and filled as mentioned above. The ore 

 in these, as in the vertical or rake vein, often bears an extremely small pro- 

 portion to the other substances occupying; the veiu. 



t I am glad to find, from the note in Dr. Boase's communication (p. 9) 

 that Mr. Fox has sug{;estcd this same notion about the formation of veins, 

 because he lias |)robab!y derived it from observation of the Cornish veins, 

 and his opinion is likely to have (and most deserveilly) far greater weight 

 with Cornish geologists, than any views emanating- from myself. 



