H. S. Washington — Ischian Trachytes. 385 



the Hawaiian basalt glass), is especially noteworthy.* This 

 brown substance seems to be identical with the " supplemental 

 spherulitic growth " of Cross (p. 424), and may be supposed to 

 represent this colloidal substance, which in the more quickly 

 cooled obsidian has not had time to crystalize, while in the 

 trachyte proper (.No. 523) it has entirely disappeared. 



In the Colorado rhyolites Cross supposes this substance to be 

 composed of hydrous silica and feldspar, in accordance with the 

 chemical composition of the rock and the intimate association 

 of quartz or tridymite with the orthoclase in the spherulites. 

 This supposition cannot be made in the case of the Ischian 

 trachytes, where the silica does not reach 61 per cent, and the 

 H 2 content is less than one per cent. Here we must suppose 

 it to have been almost entirely of feldspathic matter, with some 

 iron which went to form the trichites. 



It may be of interest to note that the ramified orthoclase crys- 

 tals described in the preceding pages, as well as the Hawaiian aug- 

 ites, show a certain similarity to the diverging pyroxene needles 

 forming chondrules in certain meteoric stones, as those of 

 Montrejeau (1858), Tadjera (1867), and Tieschitz (1878), as 

 described and shown in photographs by Meunier.f The 

 resemblance is even greater with the artificial crystals of enstat- 

 ite obtained by the same scientist and figured on page 339 

 of the work cited. 



As I have not been able to examine sections of these falls it 

 will not do to push the analogy far, and I can at present only 

 call attention to their apparent resemblance, and suggest that 

 chondrules be examined from the point of view of spherulitic 

 growth. 



* A similar brown zone may be seen about many of the spherulites in the rhyo- 

 lite of the Alter Schloss, near Schemnitz, in Hungary. 

 |S. Meunier, Les Meteorites, Paris, 1884, 240, 242, 523. 



