502 ORIGIN OF QUARTZ ROCK. 



have had decided opinions concerning it, although our writings have sometimes been 

 quoted to prove that we were even partizans in the warfare. Especially have we been 

 charged with hostility to the Taconic system of Prof. Emmons. But we have never been 

 conscious of such a feeling. Nay, if the fundamental principle of his system is that there 

 is a system of rocks below the Silurian containing peculiar fossils, we fully admit it. For 

 how does this differ from the Cambrian system of Great Britain, or the Huronian system 

 of Sir William Logan, or the analogous systems of Bohemia and Scandinavia? and 

 these may be considered as established. We are not, indeed, convinced that any of the 

 rocks of Vermont belong to the Taconic system. But if our old friend Prof. Emmons 

 shall be able to prove that they do, we shall rejoice in such a result to his indefatigable 

 efforts. We have taken pains, in another place, to give a full view of his system as we 

 have of the discussions now going on among eminent geologists and paleontologists re- 

 specting the rocks of western Vermont and Canada. We believe that much remains yet 

 to be done in this field before all the important questions shall be settled, and we 

 hope that discussions on such a subject may be conducted with candor and without per- 

 sonalities. 



The origin of quartz in the various forms in which it occurs in the rocks, raises questions 

 of much difficulty with the chemical geologist. In its pure state it is composed of silex. 

 Now silex exists in two states. In one state it is insoluble in water and most acids, except 

 the hydrofluoric, which seems never to have been concerned in geological changes. All 

 the forms of common quartz belong to this variety of silex. But there is another form of 

 this substance, when it is soluble in water and acids, and in fact " is present in all water," 

 according to Bischof. Its largest amount in cold springs is Io ^ 00 th part. It occurs also in 

 solid state, either as a powder, or gelatinous from the decomposition of silicates. 



Quartz occurs in several forms. 1. As thick deposits on beds interstratified with other 

 rocks, either in a hyaline, milky, or granular state. These masses in Vermont are 

 hundreds, not to say thousands of feet thick. 2. As veins or dykes. 3. As a constituent 

 of rocks. 4. In drusy cavities. 5. As cemented sand in sandstones. Let us see in 

 what modes these several forms may have been produced. 



1. It might be deposited from solution in water, from hot water especially, such as the 

 Geysers or hot springs. In that way quartz veins and drusy cavities may have been 

 filled. It is possible, also, in this way to account for extensive deposits. A pound of hay 

 growing upon three square feet of soil, abstracts from the soil, by means of water, 5-50^ 

 of a pound of silex. If this were deposited by the water at that rate per year, it would, 

 in 78,705 years, form a layer one foot thick. Hence, as geology always has time enough 

 at command, deposits of quartz of any thickness could in this way be formed. 



2. By the decomposition of silicates. Such decompositions may be effected in water 

 holding silicates in solution, by the action of free carbonic acid, or by organic substances, 

 which produce by putrefaction carbonate of ammonia, and this precipitates both silica 

 and alumina. In view of these and other facts, Bischof makes the sweeping assertion, 

 which, it seems to us, should be somewhat modified, that " Quartz appears in all cases to 

 be a product of the decomposition of silicates in the wet way." (Chemical and Physical 

 Geology, Vol. II, p. 479.) Such an origin agrees best with the character and arrangement 

 of quartz in granite, syenite, and some varieties of gneiss ; but we have seen that deposi- 



