180 ANNALS NEW YORE ACADEMY OF SCIENCES 



roundish cavities in an amygdaloidal zone near the surface of the older of 

 two basaltic flows. They may be divided into two groups, according to 

 mode and time of formation. On considering all the species which occur 

 in relations which permit inferences to be drawn as to relative age, the 

 following sequence was determined: 



1. Laumontite, 7. Thomsonite, 



2. Stilbite, 8. Analcite, 



3. Thomsonite, 9. Apophyllite, 



4. Calcite (yellow), 10. Calcite (colorless), 



5. Stilbite, 11. Mesolite. 



6. Chabazite, 



It will be observed that this order is different from that which has 

 been found in the Watchung sheet, but it is seen at once that several 

 species are repeated at intervals, implying irregularities in conditions 

 which would have to be explained before comparisons could be made with 

 other localities in which the sequence is normal. In such cases as this, 

 we have, perhaps, a reversal of conditions by which the circulating waters 

 which should, in the usual course of events, gradually become cooler, are 

 again highly heated. 



A somewhat similar condition is implied in the zeolitic deposits occur- 

 ring in the copper-bearing amygdaloids of Lake Superior. The sequence 

 here as determined by Pumpelly^*' was as follows : 



The chlorite of the melaphyre, and consequently the distinctive character 

 of that rock, is due to the alteration of hornblende or pyroxene. This seems 

 to have been the first step toward the production of melaphyre proper. Lau- 

 montite . . . appears to have been formed either contemporaneously with 

 the chlorite, or as the next step in the process. 



The next step appears to have been the individualization, in amygdaloidal 

 cavities, of nonalkaline silicates, viz : laumontite, prehnite, epidote, respect- 

 ively, according as the conditions favored the formation of one or the other of 

 these. 



Following these came the individualization of quartz in these cavities. 



Perhaps we may be warranted in considering these minerals, together with 

 the lime of the calcite that more rarely occurs in this portion of the series, as 

 chiefly due to the decomposition of the pyroxenic ingredient of the rock. 



So far as we may infer from the tabulated results, the concentration of 

 copper in the amygdaloidal cavities does not appear to have begun till after the 

 formation of the quartz. 



In this part of the series falls also the formation of a chloritic or green- 

 earth mineral, which in some manner has displaced prehnite, quartz, calcite, 

 and with which copper, when present, appears to stand in intimate relation. 



^* "Paragenesis and Derivation of Copper and its Associates on Lalce Superior," Am. 

 Jour. Sci., 3rd ser., vol. 2, pp. 188-198, 243-258, 347-355, 1871. 



