24 NEW YORK STATE MUSEUM 



with that of the central mass, but is separated from it by a faint 

 but sharp marginal line, which materially weakens this evidence. 



The presence of abundant cracks in the sulphides suggests yield- 

 ing to the expansive force of growing serpentine and, consequently, 

 the earlier formation of the sulphides. These cracks, however, are 

 not radial around serpentine grains but commonly occur in parallel 

 systems traversing the whole width of sections, without reference 

 to serpentine. Furthermore, it very often happens that, under the 

 strain that has produced these cracks, a core has separated from 

 the adjacent sulphide and the intervening space has been tilled with 

 the vein serpentine. It is noticeable, however, that the serpentine 

 itself is not cracked. 



Clearly, if the serpentine had a distinctive form of its own, which 

 controlled that of the sulphides, all difficulty would be removed. But 

 unfortunately this is not the case. It is true that one can not 

 examine the sections without being impressed with the conspicuously 

 rounded margins of the serpentine grains. These are so frequent as 

 to give the impression that they may be taken as characteristic and 

 peculiar to the mineral and thus, since they control the form of the 

 sulphides, establish the earlier formation of the serpentine. But 

 this conclusion is negatived by the well-known frequency of 

 similar rounded fomis of primarv' silicates in crvstalline limestone. 

 Indeed, a section of the countr}' limestone contains perfectly fresh 

 diopside in grains whose forms are precisely of the tvpe shown by 

 the serpentine (plate ii. figure i). If the surrounding calcite were 

 replaced by sulphides and the diopside then altered to serpentine, 

 the resulting relation would be just what is shown by the ore (plate 

 I, figure 2). At the same time, the latter is equally true if the 

 alteration of diopside to serpentine preceded the deposition of the 

 sulphides : which shows the difficulty of a positive determination of 

 the age relation of the minerals. If the serpentine is strictly 

 pseudomorphous after diopside, its form relation to sulphides gives 

 no light on their relative ages, since the form is that of diopside and 

 its alteration to serpentine might precede or follow the deposition 

 of sulphides, without affecting their stmctural relation. 



The most promising line of evidence leading toward a definite 

 conclusion would seem to be afforded by the replacement serpentine. 

 As previously stated, this is serpentine which is not an alteration of 

 diopside in situ with retention of form but. instead, has been 

 deposited by solutions, replacing calcite. This serpentine occurs in 

 rounded and reniform masses, often with jagged margins and with 



