1S75.] dby [Frazer. 



ascribes its formation to the deoxidizing agency of decaying organic 

 matters out of contact witli air on soluble sulphate of lime and magnesia, 

 giving rise, if carbonic acid be present, to Hydrogen Sulphide which 

 "in some conditions not well understood contains two equivalents of 

 sulphur to one of iron." He adds that he has observed that the ferrous 

 sulphide or proto-sulphide of iron in presence of a per-salt of iron loses 

 one-half of its iron, the rest being converted to Ferric Sulphide." 



It seems at least a possible explanation for this nacre promineot de- 

 termination of limonite along the edge of limestone, that by the oxida- 

 tion of the pyrites of the slates an equivalent of sulphuric acid in addi- 

 tion to that necessary to form Ferric Sulphate has been produced. That 

 this molecule of free sulphuric acid in its passage over the mica and 

 chlorite slates has dissolved out part of their alkalies, especially soda. 

 That this solution of sodium sulphate has mingled in the clay beds below 

 with the solution of calcium bicarbonate, pi-oduced by the drainage of 

 rain waters over the limestone beds, giving rise to sodium bicarbonate and 

 calcium sulphate. That this sodium bicarbonate reacting on the Ferrous 

 Sulphate has precipitated Hydro-Ferrous Carbonate which has been by 

 oxidation rapidly converted to Ferric Hydrate, while the Ferric Sulphate 

 has been immediately thrown down as hydrous oxide. This, be it re- 

 peated, is simply one of many explanations which may suggest them- 

 selves of the obssrved fact that the limonite deposits are more frequent 

 and extensive in the neighborhood of limestone deposits. 



But though the solutions from such basins may favor the deposition of 

 this ore, they are not always necessary. 



It has been incidentally stated that one proof that the supposed iron in 

 limestones was not necessary for the formation of these limonite beds, is 

 that very similar limonite beds are known to occur miles away from any 

 known outcrop of limestone. Such are the beds referred to as the Ho- 

 facker, Cameron Co., Keeny Banks, &c., &c., which occur in the lower 

 part of York county and the upper portion of Baltimore and Car- 

 roll counties, Maryland. The circumstances of occurrence alike in 

 both cases are the pyritiferous character and the highly inclined strata. 

 The former is much more coarsely porphyritic in the older beds so that the 

 hydroxidation of the pyrites has not been so perfect, and the ore is much 

 more red short than is the case close to the limestone. But the large 

 amount of pyrites in the rooks, in all stages of transition to limonite, 

 would seem to render the search for any other source of supply of iron 

 unnecessary. ^ 



r. s — VOL. siv. 



