436 Mr. H. J. Brooke on a New Ore of Silver. 



The mass of iron lias a less sectional area than the stone because 

 of its greater specific gravity, viz. in the proportion of (50'9)^ 

 to (70'6)'^; it would therefore only be projected with a velocity 

 of 372 feet per second; or as 



498436 : 259081 :: 715 : 372. 



That is, a velocity more than 20 times too small to allow of 

 the larger known meteoric masses to reach the earth, if projected 

 from a lunar volcano. 



The exclusion from a lunar origin of the larger meteoric 

 masses, especially iron ones, though not perhaps altogether 

 subversive of the lunar theory genei'ally, is j'^ct injurious to its 

 stability. 



The physical constitution and internal appearance of some 

 aerolites also, as those of Barbotan, Weston, Juvenas, and 

 Bishopville, are entirely opposed to the idea either of an atmo- 

 spheric origin, or of any consolidation of homologous, or 

 nebulous particles existing in interplanetary space. They are 

 evidently ^jrt?'^s, as Dr. Lawrence Smith likewise justly insists on, 

 of some larger whole, and are not unfrequently true igneous, if 

 not volcanic rocks. Physically speaking, there is little choice 

 left to us but to consider some of them certainly as having 

 true geological and mineralogical characteristics ; either pro- 

 ceeding from volcanoes iu the moon, or portions of a broken 

 satellite or planetary body : there may indeed be difficulties and 

 objections to either supposition. 



In a previous Number of this Journal, I endeavoured to 

 bring forward some arguments and facts iu favour of the 

 latter idea, and I barely alluded to the lunar theoiy, but since 

 the publication of Dr. Lawrence Smith's elaborate essay in its 

 favour, I have now ventured to state more fully some reasons, 

 not without their weight, against a theory in many respects 

 so plausible. 



LXIL On a New Ore of Silver. By H. J. Brooke, F.R.S..* 



I RECEIVED some years since from Mexico a specimen of 

 an ore of silver, said to be carbonate. It occurs in small, 

 compact, irregular-shaped, earthy-looking masses, imbedded in 

 carbonate of lime and quartz accompanied by crystallized blue 

 carbonate of copper. Its colour is dull, dark gray ; it is entirely 

 devoid of lustre, and its hardness appears to differ in different 

 parts of the specimen. 



* Communicated by the Author. 



