Montreal Natural History Society. 2^5 



From good data, Professor H. A. Newton, of Yale College, has 

 calculated tliat they proceed from an elliptical ring, which has a 

 period of revolution of 281 days, and through which the earth 

 passes about this time, occupying three or four days, showing that 

 this belt must be several millions of miles thick, and must contain, 

 at a moderate calculation, more than three hundred millions of small 

 meteoric bodies. 



Now the earth at this time is advancing through space at the rate 

 of about two millions of miles a day, and the bodies of this ring, 

 having a retrogade motion, enter our atmosphere with immense 

 velocity. The ordinary height of these luminous meteors is from 

 lifty to seventy miles, and the rare atmosphere at that height opposes 

 sufficient resistance to these rapidly moving bodies to heat them to 

 whiteness, and even convert them into vapour. The latent heat of a 

 given bulk of this rare atmosphere is as great as that of the same 

 bulk of more dense air near the earth, and calculations show that a 

 meteor, moving at a rate of only ten miles a second, or less than 

 one-half the ordinary velocity of these bodies, at a height of thirty- 

 four miles, would in one second's time evolve heat enough to make 

 its mass white hot. The real luminous appearance comes, however, 

 from the atmosphere condensed before the moving body, and from 

 the matter of this converted into gas by the intense heat. If not 

 already dispelled in vapour, these bodies,on reaching the lower region 

 of the air, cease to be luminous from the very density of the 

 atmosphere. — Montreal Daily News and Gazette. 



coi2-E,:ESi=oisrx):E3n^CE3. 



ON THE ALLEGED HYDEOTHERMAL ORIGIN OF CERTAIN 

 GRANITES AND METAMORPHIC ROCKS. 



To the Editor of the Geological Magazine. 



Dear Sir. — The letter of Mr. James Geikie which appeared in 

 your last number obliges me to send a few lines in reply. 



I may premise by stating that my communication, " On the alleged 

 hydro thermal origin of certain granites and metamorphic rocks," owed 

 its appearance in print, solely to the fact of the Memoirs therein 

 referred to, having emanated from the pen of a member of the 

 Geological Survey of Great Britain, and it was the official position of 

 the writer which alone caused his j)roductions to be submitted to the 

 severe, but just, criticism which therein appeared. 



Mr. James Geikie, in his reply, takes me to task for so con- 

 founding him with the Survey; independent of his being actually 

 an officer of the Survey, it will be seen, upon reference to his own 

 memoir,^ that after stating that the Geological Survey (represented 

 by himself and his colleagues. Dr. Young, and Mr. A. Geikie) was in 

 1865 extended to the district in question ; Mr. James Geikie an- 

 nounces the object of his memoir in the following words : — 



"With Sir Eoderick Murchison's permission, some of the more 

 ^ Quart. Journ. Geol. Soc, vol. xxii. p. 514. 

 VOL. rv. — Ko. XXXV. 15 



