TRANSACTIONS OF WAGNER 
MINERALOGY OF THE NEWARK GROUP IN PENNSYLVANIA 
22 
ORIGIN OF DATOLITE AND THE ZEOLITES 
HE origin of the zeolites and associated secondary minerals in igneous 
rocks has in the past been the subject of considerable discussion, and a 
wide difference of opinion appears still to prevail. Apartfrom the purely 
igneous mode of formation claimed by the earliest writers, and the contact- 
metamorphic origin advocated by Bunsen, the theories may all be grouped 
under two general classes, —first, attributing their formation to waters accom- 
panying the eruption of the magma, and second, ascribing them to the subsequent 
action of circulating waters, of meteoric origin. 
As principal exponents of the former view may be mentioned Beck, 
Hawes,’ Professor В. K. Emerson," and Professor J. V. Lewis; while the 
latter has been defended by J. D. Dana," Fischer," Professor R. Brauns," 
and President C. R. Van Hise.” 
The evidence favoring the former consists in— 
(1) The fact that considerable water does accompany every eruption, and is 
given off as the magma solidifies. 
(2) The fact that fluorine and boron are frequently present in the minerals in 
question, these elements being usually of magmatic origin. (Emerson.) 
(3) The fact that the waters effecting the decomposition of the original rock 
and the development of the new minerals must have been free from oxy- 
gen, in that ferrous iron was not changed in the process. (Hawes.) 
(4) The fact that the minerals first deposited are usually anhydrous, and the 
degree of hydration increases in the successive layers. 
In opposition to these views it may be objected :— 
(1) That zeolites are not known to form in modern lavas at the time of their 
extrusion, even though abundant water is present. (Dana.) 
(2) That the fluorine and boron might be derived by the decomposition of 
primary minerals containing them, such as tourmaline or danburite. 
(Fischer. ) 
(3) That removal of oxygen dissolved in surface waters would be accomplished 
in the upper layers of the rock,—the belt of weathering. (Van Hise.) 
(4) That the composition of the new minerals formed may well be determined 
by the chemical character of the solution rather than by the tem- 
perature. (Brauns.) 
