126 NEW YORK STATE MUSEUM 



all coming from the dumps. The study of the exposures has led 

 us to the belief that the balls may have had a glassy crust origi- 

 nally, and that this has been sheared free from them by subsequent 

 movements. At present all glassy material is between the balls 

 and most of it has been much crushed by shearing. 



Thin sections from the rock of the balls show a network of 

 minute feldspar laths set in what is certainly in some cases, and 

 probably in all, a glass base. In the finer grained rock from the 

 margins of the balls the laths have a prominent radialor spherulitic 

 arrangement. The somewhat . coarser rock from the centers has 

 the same arrangement, but less prominently. The laths are minute 

 and not greatly twinned. In the coarser varieties extinctions up 

 to 20° are shown and the feldspar is probably andesine-labradorite. 



In none of the slides is there any determinable pyroxene, nor 

 anything which especially suggests altered pyroxene. In the finer 

 grained rock it is quite certain that no pyroxene ever crystallized 

 out; in the coarser rock some may perhaps have done so, as there 

 are small scattered patches of calcite and possibly alteration 

 products between the feldspars which may have resulted from 

 pyroxene alteration. But we regard it as most probable that the 

 stage of crystallization of pyroxene had not been reached in any 

 of the rock at the time of solidification. 



All the slides show occasional, sharply bounded areas which 

 have the outlines of porphyritic crystals. A number of these seem 

 quite certainly original olivines ; the outer form and the angles 

 are precisely those of that mineral. This has led to the belief 

 that all are probably original crystals of olivine. They show three 

 different types of alteration. 



In type i the mineral is entirely gone to a fine, light greenish, 

 feebly polarizing aggregate, which seems unquestionable chlorite. 

 A few individuals show traces of a mesh structure which suggests 

 serpentine, but this is by no means the rule. This is the more 

 usual alteration. 



In type 2 the original mineral is entirely replaced by calcite, 

 fairly coarsely crystallized, or else by calcite and quartz. This is 

 the same mineral combination found in the amygdules. 



Type 3 is the least common and seems to be a further stage of 

 the alteration shown in type i. The material is either brown and 

 wholly opaque, or else this with the addition of tiny, colorless 

 patches which show faint double refraction. 



