104 ANNALS NEW YORK ACADEMY OF^ SCIENCES 



SOURCE OF THE WATERS WHICH EFFECTED KECRYSTALLIZATION AND OF 



THE NEW MINERALS DEPOSITED 



The query arises as to the origin of the circulating waters, whether 

 meteoric or magmatic. The writer adheres strongly to the views enun- 

 ■ciated by J. F. Kemp and other authorities that in the majority of metal- 

 liferous deposits the metallic minerals are almost wholly, and the solu- 

 tions largely, of magmatic derivation. In the case of these zeolitic 

 deposits, however, several lines of evidence lead to the conclusion that the 

 waters were of extraneous origin. Field observation shows that the 

 secondar}^ alteration extends to within a few feet of the lower surface of 

 the trap sheet, and points to the uprise of waters from the underlying 

 shales. In its theoretical aspects, the situation is distinctly different from 

 that of mineral veins. In the latter case, it is conceived that underlying 

 masses of fused material, slowly cooling and crystallizing, give off various 

 emanations which are forced to rise to the surface either through channels 

 in the overlying rock, or through fractures in previously consolidated 

 portions of the same mass, toward which the emanations are driven in 

 their effort to find vent. 



In surface flows, however, there is little obstruction to the escape of the 

 vapors into the open air. It can hardly be conceived that the evolution of 

 vapors from surface flows continues long after the complete consolidation 

 of the magma, for the process of crystallization necessarily excludes the 

 gaseous material. The structure of the "Watchung sheet, in the situation 

 which we are considering, indicates that consolidation was almost simul- 

 taneous with accumulation and, consequently, that the emanation of 

 vapors must have ceased shortly after the termination of the flow. On 

 this point, the following quotation from Professor Ivemp's article on "The 

 Eole of the Igneous Eocks in the Formation of Veins" ^^ is pertinent. 



The vapors contained in surface-flows of igneous rock pass off directly into 

 the atmosphere, and therefore do no geologic work of this character. The 

 most that could be expected of them would be small incrustations in the 

 cracks in their upper and first chilled portions, such as the copper minerals 

 and specular hematite found in the crevices of Vesuvian lavas. 



The greater number of the secondary minerals are traceable to the 

 primary minerals of the magma. Pectolite, prehnite, amphibole, the 

 zeolites, hematite, chlorite etc., contain only elements which are present 

 in feldspar, diopside and magnetite. There are others, however, such as 

 datolite and various metallic sulphides, containing elements that are only 



Trans. Am. Inst. Min. Eng., vol. 31, pp. 169-198, 1901. 



