Earth's Rocks to Meteorites. 239 



the carbon and leaves the iron free. The smallness of the 

 comets should not then be an objection to considering the 

 meteoric stones and irons as pieces of comets. There is no 

 necessity of assuming that they were parts of a large mass 

 in order to provide an intensely heatad birth-place. 



But although great heat was not needed at the first for- 

 mation, there are many facts about these stones which 

 imply that violent forces have in some way acted during 

 the meteorite's history. The brecciated appearance of 

 many specimens, the fact that the fragments in a breccia 

 are themselves a finer breccia, the fractures, infiltrations 

 and apparent faultings seen in microscopic sections and by 

 the naked eye — these all imply the action of force 



M. Daubre'e supposes that the union of oxygen and silicon 

 furnishes sufficient heat for making these minerals. If this 

 be possible, those transformations may have taken place in 

 their first home. Dr. Eeusch argues that the repeated 

 heating and cooling of the comet as it comes down to the 

 sun and goes back again into the cold, is enough to account 

 for all the peculiarities of structure of the meteorites. 

 These two modes of action do not, however, exclude each 

 other. 



It has been assumed that the cometic fragments go- con- 

 tinuously away from the parent mass so as to form, in due 

 time, a ringlike stream of varying density, but stretched 

 along the entire elliptic orbit of the comet. The epochs of 

 the Leonid star-showers in November, which have been 

 coming at intervals of thirty-three years since the year 

 902, have led us to believe that this departure of the frag- 

 ments from Tempel's comet (1866, I) and the formation of 

 the ring was a very slow process. The meteors which we 

 met near 1866 were, therefore, thought to have left the 

 comet many thousand years ago. The extension of the 

 group was presumed to go on in the future, until, perhaps, 

 tens of thousands of years hence, the earth shall meet the 

 stream every year. 



Whatever may be the case with Tempel's comet and its 

 meteors, this slow development is not found to be true for 

 the fragments of Biela's comet. It is quite certain that the 



