256 THE PENOKEE IRON-BEAEING SERIES. 



a thick bed of loose sandstone must be enormous; yet it is absolutely 

 certain that such cementation has occurred again and again. Silica in sili- 

 cates, in the amorphous forms, and even in a quartzose condition, is soluble 

 in alkalies, although with great difficulty in the latter case. Professor Sollas, 

 in a paper already alluded to,- has drawn a sharp distinction between 

 organic and mineral silica, the first being easily soluble, while the latter 

 is relatively insoluble. Probably most of the silica, even in the cherty 

 carbonates, would fall in his class of mineral silica ; but a part of it is 

 amorphous, and a portion of it certainly is quite readily soluble, as shown 

 by actual laboratory tests with caustic alkalies. In accounting for this 

 increase in the (juantity of silica, we have explained its relatively coarsely 

 crystalline character and the presence of the veinlets; for in the silicifica- 

 tion of the rock, as explained, these are the phenomena which we would 

 expect to find. 



The genesis, then, of tliese ferruginous cherts has been something as 

 follows: The rot'k originally occupying the place now taken by them Avas a 

 cherty. iron carljouate. Percolating solutions have decomposed a part of 

 the siderite and at the same time have taken up another part. This iron 

 carbonate has been in other places ])eroxidized and precipitated in Ijauds and 

 shots. Silica, at the same time or subsequently, has been taken into solu- 

 tion to a greater or less extent, and in other places, under different condi- 

 tions, has deen deposited as chert. Incoming solutions huxe brought with 

 them a further amount of silica, which has tilled the spaces left by the 

 removal of the carbonate. It is probalile that the peroxidation and removal 

 of iron cai-bonate and the deposition of silica have to some extent been 

 sinudtaneous; but it seems to be the case that they have in general been in 

 part succe.ssive — that is, the first process began before the second and was 



Minenil Springs of tlio United State.'!, .\ll)prt C Peale. ; No. 47, Anal.v.sps of Waters of the Yellow.stoiie 

 National Park, with an Aeconnt of the Methods of Analy.sis i'inph).ved, Frank An.stin (iooch and 

 .James Edwaid Whitlield; No.S, On snondary Kniarjjenieiit of Mineral Fragments in eertain Rocks, 

 K. n. Irving and ('. K. Van Hise. 'V\u- rre-Camlirian Roeks of the Hlaek hills, C. R. Van Hise; Rull. 

 (ieid. Soe. of America, vol. 1, pp. lil'd-lil'l. Hulletin No. 17 gives over forty water .analyses, in all of 

 which siliea is found. In m.iny il constitntes 25 <ir more per cent of the total solnhle material, 

 while in oni' ease, it rnns as high as ."lO per cent. 



-Prof. W. .1. Sollas: On the Flint Nodules of the Trimiilingham Chalks; Auual-s Nat. Hist. 

 1880, jip. 3S 1-395 ; WT-ltil. 



