Meteorite Colisection — Handbook and Catalogue. 27 



The principal objection to the first view, pointed out by Wads- 

 worth, is that fragments of pre-existing rock ought to show the con- 

 stitution of the rock as a whole instead of a specialized structure. 

 That to the second, pointed out by Merrill* in the case of the San 

 Emigdio meteorite at least, is that the great variety of forms under 

 which the minerals of a single stone often appear, make it impossible 

 to conceive of them as crystallizing from a single magma. 



It is evident that no positive answer can be given to the question 

 as yet and it may be that the conditions under which the various 

 structures have been produced have been essentially different. 



The matrix or mass of the stone in which the chondri are imbed- 

 ded is usually made up of consolidated mineral splinters such as 

 might have been produced by the breaking down of the chondri them- 

 selves. It is occasionally, however, of a glassy or amorphous nature. 



The structure of aerolites not chondritic is frequently brecciated 

 (Weston, 223, Taborg, 335) i. e.,made up of rock fragments cemented 

 together, while others seem to have undergone metamorphism subse- 

 quent to their consolidation (Chantonnay, 232). 



Evidence of physical change subsequent to consolidation is given 

 by the slickensided surfaces observable in many meteorites (Linn Co., 

 255, Kesen, 267, Bath, 351). 



These are smooth, polished surfaces seen in different portions of 

 the mass and are analogous to those found along faults in terrestrial 

 rocks. They indicate a slipping or gliding of one portion of the rock 

 on another after it had become cooled and solidified. 



In the Puquios meteorite, which has a mass wholly metallic, a 

 distinct faulting was observed by Howell. As some of the Toluca 

 irons were found to become extremely friable on heating, it is prob- 

 able that this faulting might have taken place during the passage 

 of the mass near the sun or some other hot body. 



Veins are found penetrating the mass of many meteorites (Char- 

 son ville, 230, Waconda, 310, Mocs, 323). These are frequently filled 

 with metal (Schonenberg, 254, Washington Co., 327, a) and in this 

 case may have been produced as suggested by Preston by flowing of 

 the molten metal into fissures made by cracking of the mass during its 

 passage through the air. Others, however, contain opaque, graphitic 

 or amorphous substances which probably segregated previous to the 

 entrance of the meteorite into the earth's atmosphere. 



A class of meteorites in the formation of which igneous agencies 

 could have played little part are those known as carbonaceous. These 

 are black, very friable bodies having a specific gravity not over 2.00 



•Proc. U. S. N- If. No. 11, 1888. 



