1804. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



655 



chloric acid. Below is given the results of a bulk analysis of the rock 

 as made by Mr. Eakins: 



SiO., 



TiO, . 



AI2O3 



CraO, 



Fe,03 



FeO . 



MnO. 



NiO.. 



CaO.. 



MgO. 



Per cent. 



46.13 



.73 



4.69 



.04 



.73 



16.87 



Trace. 



.09 



4.41 



25.17 



Per cent. 



BaO Trace. 



K-jG Trace. 



IS'ajO i .08 



HjG I 1.38 



P2O6 .07 



S .24 



Specific gravity. 



100. 03 

 3.35 



Saxonite; Harzhurgite. — From dike between North and South Meadow 

 creeks. This rock (Ko. 62402, U.S.N.M.) was first noticed on the west- 

 ern side of the divide between North and South Meadow creeks, wliere 

 it cropped out by the roadside in the form of a sheet not over 50 feet in 

 width, of a plainly laminated deep green serpentinous rock lying in the 

 gneiss, and apparently corresponding with it in dip and strike. The 

 outcrop was traced in a southerly direction toward South Meadow Creek, 

 finally disappearing at the lake branch of the creek. Everywhere the 

 rock had the appearance of a highly tilted metamorphic schist, except 

 at the extreme southern terminus, where it widened out into a bulbous 

 enlargement which was serpentinous on the margins, but showed a 

 nucleus of a dense dark gray, very tough, and hard rock made up of a 

 macroscopically irresolvable groundmass thickly studded with imper- 

 fectly outlined phenocrysts ox a pyroxenic mineral with a bronze luster. 

 The conditions of the rock were such as to at once suggest that this 

 nucleus represented the unaltered portion of an original eruptive mass 

 from which the schistose serpentine had been derived by chemical and 

 dynamic agencies. This suggestion was substantiated by chemical and 

 microscopic examination. 



The rock from the southern end of the dike, in its least altered con- 

 ditions, shows under the microscope a dense groundmass of finely gran- 

 ular colorless rhombic pyroxenes and pale brown almost colorless horn- 

 blendes, interspersed with a few olivines, the usual sprinkling of iron 

 oxides, and small rounded forms of dull green pleouast. Throughout 

 this ground mass are scattered the bronzite i)henocrysts above noted, 

 more rarely irregular olivines, occasionally very irregular plates of 

 faintly brownish or greenish hornblendes and more rarelj^ shreds of 

 a deep red-brown mica which show extinction angles of about 3'^, when 

 measured against cleavage lines in cross sections. In but one or two 

 instances were observed small granules of a basic plagioclase feldspar. 

 Bronzite and olivines make up the main mass of the rock. 



The structure of the rock is quite variable and complex, and difficult 

 to describe intelligibly. With the exception of certain of the horn- 

 blendes of the groundmass, none of the constituents show good crystal- 



