46 CALIFORNIA ACADEMY OF SCIENCES. 



first consolidation ; the greenish augite is allotriomorphic 

 and partly later than the plagioclase ; associated with it 

 and surrounding it is a dark green hornblende in small 

 quantities. The principal mass consists of allotriomorphic 

 or lathlike feldspar crystals ; some prisms are plagioclase 

 with very narrow striation ; orthoclase occurs in Carlsbad 

 twins but predominating is an intimate microperthitic 

 mixture of orthoclase and plagioclase (albite?). The 

 interstices between the lathlike feldspars, mostly triangu- 

 lar spaces, are often filled with a colorless isotropic sub- 

 stance which sometimes also fills the interior of the feld- 

 spars in a curious manner. Faintly double refracting 

 spots may occasionally be noticed in the isotropic mass. 

 This interstitial mass has every appearance of glass, but 

 it might also be a tesseral mineral, perhaps related to so- 

 dalite. It dissolves easily in hydrochloric acid and gives 

 a strong Na reaction. The rock contains 5.50/' KagO 

 and 4.14/' NagO. according to determinations made by 

 Mr. E. Whittield. This rock is described on p. 723 in 

 Vol. XV, loth Census, and is there called a mica-augite 

 trachyte. 



The third, from the Highwood Mountains, is a lip;ht 

 colored coarse-granular rock in which larger feldspar 

 crystals and small green augites may be noticed with the 

 naked eye. Under the microscope: Partly idiomorphic 

 green augite and irregular foils of biotite, both rather 

 sparingly; the principal mass consists of feldspar in large 

 thick prisms, not striated but often intergrown in micro- 

 perthitic form with an exceedingly closely striated plagio- 

 clase. Between these prisms lies an allotriomorphic mass 

 of large, irregular and interlocking grains, mostly micro- 

 perthite. A partial analysis of the rock by Dr. F. A. Gooch 

 gave KagO : 5.66%, NagO : 7.88, which would seem to in- 

 dicate that the plagioclase is albite or oligoclase. This 



