Frazer.] dbo [March 19, 



which were formerly above the present surface have been washed away, 

 and with them'\heir 47,730 tons of metallic iron, or their 79,691 tons of 

 limonite (if all this iron was hydroxidized), for every 1000 feet of slope, 

 5 feet of thickness and 1 mile of outcrop. Added to the smaller contri- 

 bution of ths partially weathered slatss at the surface, this gives the 

 total of 79,711 tons of limonite per mile, which has been gradually carried 

 down the dip and segregated among the clays. But these slates are of 

 very great thickness — at least 100 times what has been assumed. Allow- 

 ing, then, for all loss by transportation into the sea, and through breaks 

 in the continuity of the clay beds to great depths under ground, and for 

 combination with the silicates to form double salts, we still have more 

 than enough to account for all the lai'gest ore banks. It will be asked, 

 why these deposits should bear so close a geographical relation to the 

 limestone basins ? An example taken from Feigley & Brillhart's bank in 

 the Dunkard Valley, one mile east of Logansville, is interesting in this 

 connection. Here is the southwest limit of the easterly portion of the 

 small limestone trough which runs parallel with and south of the greater 

 York county synclinal. About a quarter of a mile east of Brillhart's 

 works there occurs a rock almost indistinguishable from the other slates 

 but which contains ± 33 per cent, (?) of calcium carbonate. 



This indicates either that these slates have been subjected to a long 

 soakiog with calcium bicarbonate or that the deposits of the carbonate of 

 lime proceeded together with the mechanical deposition of the sediments 

 which formed the slate bed. 



In reference to the older limonite formations of Lancaster county, it i* 

 said (, Vol. I, p. 183): "An interesting inquiry is here suggested as to 

 what can have been the geological atmospheric condition which produced 

 the remarkable percolation which carried down so large an amount of ore 

 out of these ferruginous beds. Was it tepid rain charged with carbonic 

 acid in an early Palaeozoic period ? Or could it have been a long filtration 

 of surface waters such as now soak the earth ? Or are we to surmise an 

 action of internal steam issuing upwards through crevices in the strata 

 in a period of crust movement and disturbance ? I am inclined to the 

 first conjecture," 



Dr. Hunt in his essay on metalliferous deposits (XII, Chem. and Geol. 

 Essays, Boston, 1875, p. 239), says: "The question has been asked me — 

 Where are the evidences of the organic material which was required to 

 produce the vast beds of iron ore found in the ancient crystalline rocks? 

 I answer that the organic matter was in most cases entirely consumed 

 in producing these great results, and that it was the large proportion 

 of iron diffused in the soils and waters of those early times which not 

 only rendered possible the accumulation of such great beds of ore, but 

 oxidized and destroyed the organic matter, which in later ages appear 

 in coals, lignites, pyroschists and bitumens. Some of the carbon * * 

 is, however, still preserved in the form of graphite, " &c. 



With reference to the Ferric Sulphide or pyiite, the same author 



