Meteorites, and Volcanic Agency* 499 



The greater number of meteoric irons exhibit a structure 

 which indicates that each has formed part of a large mass 

 possessing similar crystalline characters. The formation of 

 large masses so constituted, presupposes, as Haidinger has 

 pointed out, long intervals of time for tranquil crystallization 

 at a uniform temperature; and these conditions could o:ily 

 prevail on one of the larger cosmical masses. On the surfaces 

 of many meteorites (such as the Chateau-Renard, Pultusk, and 

 Alessandria ones) indications resembling in every particular 

 the " slide " or " throw" of terrestrial rocks are to be met 

 with, appearances which indicate the disruption or dislocation 

 of larger masses. Other meteorites, like those of Tula, Chan- 

 tonnay, Orvinio and Weston, are congeries of angular frag- 

 ments, and correspond, as regards structure, with terrestrial 

 breccias. Many stones, moreover, are formed of very small 

 fragments, of tiny splinters, and resemble volcanic tuffs. These 

 characters, again, point to larger cosmical masses which have 

 undergone mechanical changes as the source whence they 

 have been derived. 



So far, then, it would appear that the material of which 

 meteorites consist has been furnished by one or more large 

 masses, the formation of which must have occupied a long 

 period of time. The question which therefore suggests itself 

 is, How is the process of disintegration to be accounted for ? 

 This Daubree endeavoured to solve, and arrived at the alter- 

 native that disintegration must be the effect either of impact 

 or explosion*. 



The idea that the smaller planetary bodies were formed by 

 the impact and disruption of larger cosmical masses was pro- 

 pounded by Olbers f to account for the existence of the aste- 

 roids ; and D'Arrest and C. von Littrow have in more recent 

 times established, by careful calculation, the possibility of the 

 impact of these bodies actually taking place. 



By the impact of two solid cosmical masses, moving with 

 planetary velocity, fusion, perhaps even vaporization, would 

 occur over the area of contact f; disintegration, moreover, 



* G. A. Daubree, Journal des Savants, 1870. — Meunier (Geologle Com- 

 paree, 296) seeks to escape from this dilemma by supposing a spon- 

 taneous disruption of the planetary mass to have taken place in much the 

 same way as a disk of clay crumbles on drying. Even if we allow this 

 explanation to be a possible one, the further difficulty presents itself, that 

 the fragments would continue to traverse one and the same orbit, which, 

 with the meteorites, we know is not the case. 



t Zach, Monatl. Correspondenz, vol. vi. p. 88. 



% A cosmical mass possessing a velocity of three geographical miles, 

 and by impact with another mass being brought to a state of rest, would, 

 on the supposition that all the vis viva was converted into heat and none 



2 L2 



