Aerolites or stony 

 meteorites. 



Sidorolltes or stony 

 Iron meteorites. 



Siderites or 

 meteorites. 



MERRILL SCHUCHERT 629 



"All known meteorites are composed of volcanic materials, and 

 none has shown any traces of animal or vegetable life." Many have 

 undergone metamorphism. '* They are comparable with more or less 

 compacted and altered masses of volcanic asli or tulF." Nor is 

 there prei>ent anything in the natnre of a true vein rock, a ter- 

 restrial sedimentary or a metamorphic or pumiceous one, " and noth- 

 ing in content of silica, alumina, lime or alkalies corresponding to 

 the granites." All meteorites " are of a basic nature, related closely 

 to the basalts, pyroxeuites, and peridotites among terrestrial forms." 

 (1919a :lb4; 1930:39,45.) 



Merrill arranges the meteorites into " three somewhat ill-defined 

 groups " as follows : 



Chonflritic meteorites, consistinp essentially of nilioate 

 minerals with minor amounts of tlie metallic alloys and 

 sulphides. About 00 i)er cent of ull known stony me- 

 teorites are choudritic. 



Consisting of an extremely variable network or sponge 

 of metal, the Interstices of which are occupied by the 

 silicate minerals. 



Consisting essentially of an allny of nickel-iron (5-25 

 per cent nickel) with iron phosphides and sulphides. 

 Nearly or quite devoid of silicate material. 



Chondrltic meteorites. — For what they teach, the most interest- 

 ing meteorites are the stony ones, the aerolites. These chondritic 

 meteorites have small spherical and oval grains known as chondrules 

 (from the Greek word for grain) and composed of silicate con- 

 stituents, " the formation of which alfords one of the most inter- 

 esting puzzles in connection with the origin of meteorites." 



Mineralogicall}', the chondrules are composed chiefly of olivine 

 or pyroxene. " Some are largely of an undifferentiated glass. 

 Feldspars occur but rarely except in the form known as maskelynite. 

 In addition are occasional inclosures of metal or metallic sulphides, 

 chromite or other minor constituents." (1920d:450.) 



Merrill in 191G thought that the chondrules might be looked on as 

 the solidified molten drops of a " fiery rain " or a world-making mist. 

 Later, however, after a study of all the thin sections of stony mete- 

 orites in the National Museum he changed this view, saying: 



In none of them do I find chondrules developed in the variety and perfec- 

 tion of forms existing in those meteorites which are plainly tuffaceous. This 

 fact and others . . . have led me to regard the larger part If not 

 all chondritic stones as originally tuCfaceous and owing their more or less 

 crystalline condition, where such exists, to heat and pre.ssure in a nonoxidizing 

 or even reducing atmosphere. (1920d : 4G2-403.) 



Meteor Crater. — Probably the most remarkable phenomenon 

 thought to be connected with the falling of meteorites is a crater- 

 28095—31 41 



