56 STUDIES FOR STUDENTS 



clastic or brecciated have the variations which might be expected 

 from the accidents of aggregation. The monogenic meteorites 

 may show variations from fine grain to coarse grain and vice 

 versa and some portions may contain more stone or metal than 

 others, but the general structure may be said to be uniform. 



Similarities of structure in jneteorites of different falls. — While 

 the individuals of a single fall are usually similar in structure 

 and composition those of different falls often differ so that 

 they may be easily distinguished. In comparing the meteorites 

 of a large number of falls, however, similarities are readily seen 

 which permit the grouping of several falls together as being of 

 practically identical matter. A number of classifications of this 

 sort have been made of which those of Brezina and Meunier are 

 the latest and most complete. Brezina, who makes structure the 

 leading feature of his classification, has thus reduced all known 

 meteorites to sixty-one groups, while Meunier, with whom 

 mineralogical composition is the chief criterion, makes sixty- 

 two groups. 



Degrees of coherence. — The iron meteorites are, as might be 

 expected, usually strongly coherent and tenacious to a high 

 degree of malleability. Yet there are variations in this respect. 

 The iron meteorites showing coarse etching figures can usually 

 be sawed only slowly and with great difficulty, while those of an 

 amorphous or finely crystalline character cut more readily. 

 Some iron meteorites, such as those of Coahuila and Nelson 

 county, can be broken readily by the blow of a hammer. 

 Among the stony meteorites all stages of consolidation maybe 

 traced from those of an almost flint-like toughness (Long Island) 

 to those so friable as to crumble on handling (Warrenton). The 

 majority of stony meteorites are fairly coherent so as to take a 

 good polish. 



Kinds of structure according to texture. — According to what is 

 often known as rock texture, meteorites display a number of vari- 

 ations which are for the most part entirely comparable with simi- 

 lar variations seen in terrestrial rocks and may be described by 

 the same terms. Accordingly, among the monogenic meteorites 



