134 PERIDOTITE. 



even in the feldspar. A little brownish-biotite was observed as a secondary product. 

 The structure of a portion of this section is shown in figure 2, Plate VIII. 



Another section, purchased from Voigt and Hochgesang, shows similar characters, but 

 part of the olivine and enstatite is not so much altered as in the preceding. While in 

 the former the diallage largely predominated, in this only enstatite was observed. 



A section of so-called serpentinfels of Baste, purchased from R. Fuess of Berlin, 

 shows a gray and greenish-brown sponge-like mass holding serpentinized olivines. Tlie 

 general structure is like the preceding ones described from Baste, as well as those to be 

 later given from Christiania and Gjyirud, Norway, but the alteration lias progressed con- 

 siderably further. Talc and amphibole occur as secondary products, as does a pale bluisli- 

 green mineral associated with a mineral of pale pinkish or grayish color. From their 

 association and relations the bluish-green form seems to be a better developed state of 

 the gray mineral. Since both are isotropic, and have the usual structure and relations 

 observed belonging to garnet, I am inclined to refer them to that mineral. Associated 

 with these are coflee-brown picotite or chromite grains, which also appear to be of second- 

 ary origin, and closely resemble those found in the St. Paul's pieridotite. 



No. 5041 is another specimen of the so-called schillerfels from Baste, Harz, obtained 

 from Voigt and Hocligesang. Tliis is a greenish-black rock, showing the schiller of the 

 altered pyroxenes, and holding rounded grains of serpentinized olivine. Weathered on 

 one side to a rusty-browu. The section of tliis is very similar to the one last de- 

 cribed, but contains more picotite, and none of the pale bluish-green mineral has been so 

 far observed. 



Streng states that the schillerfels of the Harz is a mixture of anorthite, protobastite, 

 diaclasite, compact schillerstein, schillerspath, serpentine, and chrome-bearing magnetite.* 



Figure 1, Plate VIII., shows a portion of the structure of an enstatite mass with its 

 enclosed olivines — the characteristic Assuring of both minerals being shown. The dark 

 grains in the olivine are picotite and the greenish portion indicates the beginning of 

 change in the enstatite. 



Figure 2 of the same plate indicates a change in the rock still further advanced, and 

 shows the olivine discolored by secondary ii'on ores bordering the fissures, and more or less 

 changed to serpentine, while the enstatite is considerably altered. Figure 5 on the same 

 plate exhibits a phase of extreme alteration, the rock, while retaining its structure, having 

 its olivine entirely, and its enstatite and diallage nearly, if not entirely, replaced by ser- 

 pentine and various secondary products. 



Chrisiiania, Norivay. 



5063. A dark, nearly black rock, showing in places the schiller of the pyroxene 

 minerals, and occasionally exhibiting grayish-white spots. At one end it presents an 

 appearance similar to that of the forellenstein of Volpersdorf One .side is coated with 

 serpentine and dolomite. 



Section : a grayish-white spongiform mass, enclosing gi-eenish, serpentinized olivines. 

 The olivine is much altered, showing the usual reticulated network of magnetite with the 

 later greenish and yellowish serpentine. Part of the olivine enclosed between the meshes 

 remains intact, or only sliglitly smoky. In some of these elongated tubes of minute size 



* Neues Jahr. Min., 1S62, p. 521. 



