129 



although many meteoric irons, some of them like that of Cran- 

 bourne (No. 77) weighing several tons, have been found at 

 various parts of the earth's surface, very few of them have been 

 actually observed to fall : in the case of the stony meteorites 

 just the opposite holds good, for they are never very large, and 

 few are known which have not an authenticated date of fall. 

 This may be due to the fact that a meteoric stone is less easily 

 distinguished than is a meteoric iron from terrestrial stones, 

 and will thus in most cases remain unnoticed unless actually 

 seen to fall ; while, further, a quick decomposition and dis- 

 integration must set in on exposure to atmospheric influences. 

 The smaller size of the meteoric stones may be due to the 

 greater ease with which they break up on the sudden increase 

 of temperature of their outer surface consequent on their 

 entry into the earth's atmosphere. The largest meteoric stone 

 known is that of Knyahinya (308 0), weighing 647 lbs. ; 

 it is preserved in the Vienna Museum. 



If we now examine more closely the forms in which the 

 various components of the meteoric stones present themselves, 

 it will be seen that in the large group of Chondritic aerolites 

 the chondra or grains, of which some can only be seen under 

 the microscope whilst others reach the size of a cherry, appear 

 to have attained to their present form not by a process of 

 crystallisation but by one of friction, and that the matrix or 

 paste in which the chrondra are enclosed is apparently made 

 up of minute splinters, probably due to the wearing down of 

 the chondra themselves. Such aerolites bear a strong struc- 

 tural likeness to volcanic tuffs, and as they contain no trace 

 of vitreous rock nor yet any distinct crystals, they are quite 

 different in character from the volcanic lavas. 



Since the time of their formation some meteoric stones, as 

 Tadjera (310 T) appear to have been heated throughout 

 their mass to a high temperature: and in Orvinio (V 336) 

 and Chantonnay (174 W) fragments are cemented together 

 with a material having the same composition, thus giving rise 

 to a structure resembling that of a volcanic breccia. Others 

 seem to have experienced a chemical change, for in Knyahinya 

 (308 0) and in Mezo-Madaras (253 T) the chondra are 

 found to be surrounded by spherical and concentric aggrega- 



