178 ANNALS NEW YORE ACADEMY OF SCIENCES 



III. Comparison with Other Deposits and General Conclusions 



With these minerals, the processes of alteration through ascending 

 waters appear to have been brought to a close. This may perhaps be 

 considered due to any one or to a combination of several causes. The 

 waters may have reached a temperature which was practically the average 

 climatic temperature of the region and were therefore unable to effect 

 further changes, or the circulation may have become much enfeebled be- 

 cause of diminution of the stores of heat-energy in the rock, or the 

 velocity of reaction at these lower temperatures may have become so 

 small that its effects are negligible. The writer is inclined to believe that 

 all of these causes cooperated. 



The general order in which the minerals appeared is shown in the 

 accompanying chart (page 179). The question arises as to the extent to 

 which this sequence should be considered an invariable one appl}dng to all 

 zeolitic deposits. In considering this, the first point which must be kept 

 in view is that the conditions under which the formation of minerals 

 occurred in other deposits must have been similar in order that the results 

 should be comparable. A frequent occurrence of zeolites is in fissure- 

 veins cutting masses of intruded igneous rock, as in the Palisades. In 

 such cases, sublimates given off by the magma at the same time that 

 processes of alteration are in progress (such as boric oxide, carbonic acid, 

 fluorine vapors, sulphur compounds and possibly others) and passing into 

 the channels of circulation must affect most decidedly the periods of 

 deposition of the compounds into which they themselves enter. Such 

 minerals as datolite, calcite, apophyllite and the metallic sulphides might 

 therefore appear at periods somewhat different from what has been ob- 

 served in the Watchung minerals. 



It has been shown, too, that the presence of boric acid in considerable 

 quantity acts as a disturbing factor, which affects the nature of the other 

 minerals deposited, and such other emanations as are capable of uniting 

 with soda and lime would probably have similar effects. On the whole, 

 however, it appears that the zeolites proper would usually follow a similar 

 sequence in such fissure deposits to that observed in the Watchung rocks. 



In zeolitic formations in surface flows of basalt, which have been 

 brought about by a similar uprise of meteoric waters, the processes should 

 normally be very similar, but it appears that in some instances interrup- 

 tions occur. From the studies of Whitman Cross and W. F. Hillebrand''^ 

 on the minerals from the basalt of Table Mountain at Golden, Colo., it 

 appears that the zeolitic deposits there occur both in fissures and in 



ESBuU. 20, U. S. Geol. Surv., 1885. 



