14 PERLITIC AKD SPHERI'IITIC STErCXUEES. [Feb. 1 894, 



with respect to that from Long Sleddale. Mr. Barker had informed 

 him (the speaker) that 'giant spherules' occurred with perlitic 

 structure inside ; in this case it was difficult to imagine the formation 

 of the spherules subsequent to the consolidation of the rock. 



Alluding to Mr. Watts's discovery of a structure resembling 

 perlitic structure in quartz, the speaker deprecated the custom, 

 somewhat rife among geologists, of giving too restricted defini- 

 tions. If a structure so like perlitic structure as to be practically 

 undistinguishable from it occurred in quartz, it might also occur in 

 other crystalline material. 



Dr. J. W. Gregory was, like Mr. Marr, not satisfied that the 

 spherulites in the Long Sleddale rock were later than the perlitic 

 cracks, as such cracks often end off against solid inclusions in the 

 glassy lava. In the Yellowstone Park cases the spherulites are 

 often old ones in a re-fused lava, and the perlites have bent round 

 them. The figure of the Buschbad case is also not conclusive, as 

 some points in the figure suggested that the perlitic cracks might be 

 the earlier. 



The Author, in reply, again pointed out what he regarded as the 

 order of sequence of the different structures in the rocks described, 

 and alluded to the sections exhibited by Mr. Watts, in which 

 a structure, seemingly perlitic, traversed crystals of quartz. He 

 doubted whether these cracks were really to be regarded as identical 

 with true perlitic structure. In reply to Mr. Marr, he stated that 

 he had never met with any case in which a perlitic fissure was 

 interrupted and abruptly cut off by a previously-formed spherulite, 

 but cited instances in which such fissures accommodated themselves 

 to the surfaces of comparatively large spherulitic bodies. He also 

 briefly replied to Dr. Gregory's remarks. 



