96 Mr, T. Sterry Hunt 



into solution by alkaline carbonates or sulpburets, have been 

 redeposited in fissures in the metalliferous strata, forming veins, 

 or ascending to higher beds, have given rise to metalliferous 

 veins in strata not themselves metalliferous. Such we conceive 

 to be in a few words the theory of metallic deposits ; they belong 

 to a period when the primal sediments were yet impregnated 

 with metallic compounds which were soluble in the permeating 

 waters. The metals of the sedimentary rocks are now however 

 for the greater part in the form of insoluble sulphurets, so that 

 we have only traces of them in a few mineral springs, which serve 

 to show the agencies once at work in the sediments and waters 

 of the earth's crust. The present occurrence of these metals in 

 waters which are alkaline from the presence of carbonate of soda, 

 is as we have elsewhere pointed out, of great significance when 

 taken in connection with the metalliferous character of certain 

 dolomites, which as we have shown, probably owe their origin to 

 the action of similar alkaline springs upon basins of sea water. 



The intervention of intense heat, sublimation and similar hy- 

 potheses to explain the origin of metallic ores, we conceive to 

 be uncalled for. The solvent powers of solutions of alkaline 

 carbonates, chlorids and sulphurets at elevated temperatures, 

 taken in connection with the notions above enunciated, and with 

 De Senarmont's and Daubr6e's beautiful experiments on the crys- 

 tallization of certain mineral species in the moist way, will suffice 

 to form the basis of a satisfactory theory of metallic deposits.* 



The sediments of the carboniferous period, like those of earlier 

 formations, exhibit towards the east a great amount of coarse sedi- 

 ments, evidently derived from a wasting continent, and are nearly 

 destitute of calcareous beds. In Nova Scotia Sir William Logan 

 found by careful measurement, 14,000 feet of carboniferous strata; 

 and Professor Rogers gives their thickness in Pennsylvania as 8000 

 feet, including at the base 1400 feet of a conglomerate, which disap- 

 pears before reaching the Mississippi. In Missouri Prof. Swallow 

 finds but 640 feet of carboniferous strata, and in Iowa their thick- 

 ness is still less, the sediments composing them being at the same 

 time of finer materials. In fact, as Mr. Hall remarks, throughout 

 the whole palaeozoic period we observe a greater accumulation 

 and a coarser character of sediments along the line of the Appa- 

 lachian chain, with a gradual thinning westward, and a deposition 

 of finer and farther transported matter in that direction. To the 



♦ Quar. Jour. Geol. Soc, vol. xv, 580. 



