76 THE SIDEROLITES A^B PALLASITES. 



is rough, splintery, and conchoidal. The rock gelatinizes with hydrochloric acid, even 

 in the cold, and gives a titanium reaction. 



Section : A granular grouudniass, composed of olivine and magnetite, holding porphy- 

 ritically inclosed feldspar crystals. The magnetite forms more or less connected spongi- 

 form irregular masses. The olivine is in crystals and grains, united directly without any 

 cement, and occupies the cells and interspaces between the magnetite masses. Grains of 

 magnetite are of frequent occurrence in the olivuie. The olivine is traversed by numer- 

 ous fissures, and the majority of the grains show a well marked cleavage. The fissures 

 usually have a ferruginous staining. Besides this, the olivine is comparatively clear 

 and unaltered, exhibithig, however, in connection with the feldspar, a greenish alteration- 

 product. 



The plagioclase is in grains and irregular masses, which occasionally send tongues out 

 into the olivine magnetite mass. It shows well marked cleavage planes, and is some- 

 what kaolinized along those lines, otherwise the feldspar is clear and glassy. In polar- 

 ized light the larger feldspar masses were seen to be made up of several polysynthetic 

 individuals. Some small microscopic grains of feldspar are scattered in tlie rock mass, 

 but as a rule most of it is in large crystals, clearly seen macroscopically. A few reddish- 

 brown biotite flakes were observed in the feldsjjar. 



The sponge-like structure of the magnetite is the same as that of the iron in the sup- 

 posed meteoric pallasites, and in a similar manner contams the inclosed olivine. As 

 would be expected, as a rule, in any iron coming to the surface of the earth in a heated 

 condition (eruptive), the iron in this rock has suffered the first stage of oxidation, and is a 

 magnetite. The writer regards the state of the iron (its alteration) of but little conse- 

 quence, so long as the structure and general chemical and mineralogical composition 

 remain the same. This section is figured in Plate I. figure 5. 



In this figure the black portions represent the magnetic iron, and the light yellow 

 and whitish portions the fissured ohvine. 



No. 999 is, both in the hand specimen and section, similar to the preceding. 



No. 1000. This is weathered to a slight extent only, and shows the same characters 

 as the unweathered portions of Nos. 998 and 999. The sections show the same relation 

 of the magnetite and olivine as in the preceding. The latter mineral contains many 

 grams and crystals of magnetite, and is niucli fissured. These fissures are filled largely 

 with magnetite granules and air cavities. It is stained yellowish and greenish in places, 

 and was seen in some portions to have been changed into a greenish aggregately polariz- 

 ing mass. 



The feldspar is clear throughout the greater portion of the mass, but in parts is 

 kaolinized, and contains fluid and air cavities. This mineral in one section is seen to be 

 in small masses, as well as large, and holding such relations to the olivine and magnetite 

 that it leaves no doubt that it is a later crystallization than either of the other minerals. 

 A small fracture extends across a portion of the section, through the feldspar and olivine 

 grains, forming a miniature vein. The materials deposited in this vein vary according to 

 its position, whether in the feldspar or in the olivine, but, at the contact of the two 

 minerals, contains ingredients derived from both. Tliis might be taken on a miscroscopic 

 scale to illustrate the variation of veins in passing from one rock to anotlier. In the 

 ohvine the vein is filled with serpeutinous material, but in the feldspar with silicious. 



