FENNER, THE WATCHVNG BASALT 181 



Subsequently to this came the individualization of the alkaline silicates, viz : 

 analcite, apophyllite, orthoclase. Here also seems to belong the formation of 

 datolite. . . . 



The fact that calcite occurs at almost every step in the paragenetic series 

 and forms one of the most common of the secondary minerals is proof that 

 carbonic acid was very generally present throughout the vphole period of meta- 

 morphism ; it was probably the chief mediating agent in the processes, with- 

 out being sufficiently abundant to prevent the formation of silicates. 



In this series again, the sequence is quite different from that observed 

 in the Watchung rocks. Pumpelly, however, has hardly touched upon the 

 question of the conditions under which the secondary minerals originated, 

 especially as regards attitude of the beds, and those who have paid some 

 attention to these matters have considered it rather from a theoretical 

 standpoint than from internal evidence. Portions of the copper-bearing 

 series are now buried to a depth of several thousand feet, and an unknown 

 thickness has been removed by erosion from their upper surface. Such 

 facts as the not unusual paramorphic change of laumontite into ortho- 

 clase might be considered to imply a reversal of the progress of alteration 

 brought about by deep burial subsequent to a cycle of alteration in a 

 more superficial zone. A detailed investigation of these deposits, which 

 would include a review of former evidence in the light of more recent 

 knowledge and a consideration of additional evidence brought to view in 

 the depths to which mining operations have now penetrated, would be 

 most interesting and valuable in throwing light on the difficult question 

 of the origin and circumstances of precipitation of the native copper. 

 Until more information is available regarding the conditions of deposi- 

 tion of the secondary minerals in the Lake Superior rocks, they will 

 hardly afford a basis of comparison as regards sequence with the 

 Watchung series. 



There are undoubtedly numerous zeolitic deposits in which conditions 

 of formation were closely analogous to those prevailing in the Watchung 

 rocks, but, as was remarked in the early pages of the present paper, few 

 observers appear to have made detailed observations regarding the se- 

 quence in which the minerals were deposited. Instances have been met 

 also, in going through the literature, which bear internal evidence of 

 rather hasty Judgment in drawing conclusions as to sequence. This does 

 not appear surprising from the misleading character of the evidence en- 

 countered in some instances in the study of the Watchung rocks, which 

 has brought into prominence the necessity of constant caution. 



In Hintze's "Handbuch der Mineralogie" a compilation is made of a 

 great number of occurrences of the zeolites, with short summaries of the 



