312 Scientific Intelligence. 



blende, is called an augite-traehyte. It resembles in general com- 

 position the augite-syenyte of'vom Rath, which constitute the 

 larger part of fit. Monzoni in the South Tyrol. Other localities 

 arc mentioned of trachyte and of this augite-trachyte. 



Rhyolyte was so named by Richthofen in 1860. It was made 

 to include certain trachyte-like or felsitic and more or less glassy 

 rocks which contained disseminated quartz, and bore " clearer evi- 

 dence than other rocks of having once flowed in a viscous state.*' 

 The more or less glassy kinds comprise obsidian, pearlstoue, and 

 pumice. These Zirkel designates glassy rhyolyte. Other kinds. 

 I io, not appearing glassy, but show 



ngafluidal - ingi dienN irranged 1 par- 



allel wavy bands, instead of even-grained, as seen in microaeopk 

 sections, he designates proper rhyolyte; and certain era 

 kinds (not observed among the rocks of the 4oth parallel) he calls 

 neoadyte. Rhyolyte is found at several places in Nevada, and 

 many \ trieties are particularly described and figured. They some- 

 i or grains as large as 

 peas. In some the structure is tine granular throughout ; in others. 

 there are glassy lines or patches; in others, spherulites ; and some 

 are glassy throughout. 



Augite-andesyte contains over 58 per cent of silica— in this dif- 

 fering from most igneous augitic or pyroxene rocks. A variety 

 from west of Basalt Creek, Washoe, is brownish-black, somewhat 

 resinous in luster, with "white feldspar crystal- which 

 tabular," and contains hyalite in its amygdaloidal cavities and 

 fissures. The base is partly glassy. The feldspar is partly ortho- 

 clase (sanidin) in twins, and partly a triclinic species, t 



'' g. The percentage of silica was found to be 58-015. 

 k has been observed on Teneriffe, Java, Chimborazo, 

 in Hungary, etc. Augite-andesyte is near the melaphyre of some 

 lithologists, but differs in the base being partly glassy. It shows 

 its relation to basalt by containing some chrysolite. The rock 

 also occurs red, blackish, and of other colors. 



Basalt is described from various localities. In a vaii 

 Kaw-oii Mountains, having a structure "intermediate hetw. > n tin 



cro-porphyritic and the even-grained," microscopic aggregations 

 tridymite crystals were observed, in the form of thin hexagonal 

 piates, partly overlapping like tiles and parti v in groups. This 

 is the first time tridymite has been met with in basalt : and it is 

 remarked that " since the basalt comes to the surface through or 

 near strata of intiiM.riai silica, it is not impossible, as Mr. Clarence 

 King has suggested, that an included fragment of this silica may 

 be the source of the tri \ mite, n \ i,,, | case it would of course 

 be a substance originally foreign to basalt." 



Leucite rocks are described from the Leucite Hills, northwest ot 

 Point of Rocks, Wyoming Territory. Tin-van- ii-ht vel!owi-h- 



n !■• ■ ks, \ rj rich ',,, . \ ,-r, erpl lis, i 

 augite in grains yet sparingly, with no feldspar of any kind. 

 They thus differ widely from the European leucite rocks. 



