r22 



NEW YORK STATE MUSEUM 



Several details of the rock structure remain to be noted. 



Jointing of the lava crusts. The globular surfaces of the lava 

 crusts of the balls are beset with a network of cracks perpen- 

 dicular to the surface. The general appearance of these joints 

 as they are revealed on cross sections of the structure, is shown 

 in figure 3. On exposed walls, the lava crusts frequently fall to 

 pieces in short polygonal joint columns similar to basaltic 

 columns. 



So far as I have seen them, these joints do not penetrate the 

 scoriaceous interior of the balls or the limestone inclusions ex- 

 cept it be in one or two cases of the latter rock, as shown in fig- 

 ure 4, where dikelets cut across the inclusions. 



Fig. 4 Sketch of an included, partially absorbed block of limestone, showing two 

 dikelets. 



These dikelets are in all cases conterminous with the crusts 

 of dark, dense rock surrounding the limestone. In one instance 

 as many as three parallel cracks in the limestone inclusion have 

 thus been filled. These inclusions are notable at the north- 

 eastern corner of the knob. 



The inclusions of limestone point to an irruption through the 

 lower paleozoic limestones which must occur in this field beneath 

 the Hudson terrane. It is questionable whether the present 

 color of the limestone can be taken as evidence of the original 

 rock having been a white crystalline limestone, since the organic 

 matter which gives the dark color to the Lower Silurian lime- 

 stones of the upper Hudson valley would be driven off in the 

 heating of the rock. The inclusions may be appealed to as evi- 



