244: Scientific Intelligence. 



and Calcitic Gold Silver Veins, and is illustrated by the gold 

 quartz veins of California. Some of the conclusions of the paper 

 are as follows: Almost all lissure veins are bordered by altered 

 zones, the character of the alteration differing widely in different 

 veins ; that the alteration usually consists in the loss of certain 

 constituents and the introduction of new elements, chiefly C0 2 and 

 S ; that the processes are such as can only be explained by 

 aqueous agencies acting under high pressure, temperature and 

 concentration while ascending along the fissure ; that these 

 ascending waters are chiefly surface waters. which after a cir- 

 cuitous underground route have found in a fissure an easy way to 

 return to the surface ; and that most fissure veins are genetically 

 connected with bodies of intrusive rock which on cooling give off 

 volatile compounds of the heavy metals which on sizing meet 

 surface waters and are carried along by them and subsequently 

 deposited by their aid in the veins. w. e. f. 



8. Some Iowa Dolomites • by Nicholas Knight. (Communi- 

 cated.) — The rocks herein described were analyzed in the chemical 

 laboratory of Cornell College under the direction of the writer. 

 The composition of the rocks varies from nearly typical dolomite 

 to admixtures in different proportions of calcium carbonate and 

 dolomite. 



(1.) This is a bluish-drab saccharoidal rock, situated near the 

 base of the Iowa Devonian series, at Rochester, Iowa. It is of 

 special interest because locally believed to contain silver. A 

 miner's shaft, thirty feet deep, has been sunk to it, and several 

 analyses are said to have been made, showing a large amount of 

 silver. Professor W. H. Norton, of the Iowa Geological Survey, 

 was unable to authenticate any of the analyses. He found no 

 geological grounds for the slightest suspicion of any precious 

 metal in these beds. This analysis was made not to disprove the 

 presence of silver, but to show the lithological change from the 

 subjacent dolomites of the Silurian. The specimen was analyzed 

 by Miss Minerva Herrinton, A.B. 



CaC0 3 . 78-75 per cent 



MgC0 3 .. 20-16 



Fe 2 0„ and A1 2 3 0-10 



Si0 2 _. 0-4 



MnO„ 0-2 



99-61 



The rock varies widely from a true dolomite, which contains 

 CaC0 3 54-35, MgC0 3 45-65. 



(2.) The Coggon beds as described by Professor Norton in the 

 Reports of the Iowa Geological Survey, overlie the Gower stage 

 of the Silurian, and are immediately beneath the Otis beds of the 

 Wapsipinnicon stage, — the lowest Devonian terrane recognized 

 in Iowa. The lithological affinities of the Coggon are with the 

 Niagara, but the very meager fauna inclines rather toward the 

 Onondaga limestone of the Devonian. The specimen from 



