Correspondence. 141 



of an article similar, yet far inferior in beauty, and utterly without 

 variety ; whereas this rock produces not less than ten or twelve 

 distinct kinds." This beautiful stone is still as much neglected as it 

 was in the lime of M'Culloch. If a market were found for it, it 

 might be quarried close to deep water, where vessels might ride and 

 load in safety ; and the works would be earned on with the advantage 

 of every facility that the ov^nier. Sir Lewis Campbell, would willingly 

 afford. 



Dui-ing the few short hours that I could devote to a ramble over 

 Davar, I found the attractions of the porphyritic rocks to be so 

 seductive, that the hammer was much more frequently in use than 

 the gun. — I am, Sir, yours obediently, 



Edwin Buowisr, P.G.S. 



Bukton-on-Trent, Felruary 13, 1866. 



GEOLOGY OP THE MOON. 

 To the Editor of the Geological Magazine. 



Sir, — I have no doubt many of your readers will thank you for 

 introducing the subject of the Moon into the Geological Magazine. 

 The letter of Mr. Birch on Lunar Glaciers ought to lead to observa- 

 tions and speculations calculated to enlarge our knowledge of the 

 present and past condition of the moon's surface. That glaciers to 

 a limited extent may now exist, and that traces of former glacial 

 action may be discovered on the surface of the moon, does not appear 

 to be a very extravagant assumption. But few astronomers would 

 probably be disposed to concede that all the white parts of the moon 

 are Snow and Ice. The absence of an atmosphere (beyond a possible 

 shallow gaseous envelope) would at first sight appear to be incom- 

 patible with a belief in a general glacial condition of the lunar 

 surface. It is however for the photo-selenologists to inquire whether 

 the modern theory of the moon advocated by Professor Hansen and 

 others will afford him any support. This theory implies that the 

 farther or unseen hemisphere of the moon is a comparative depres- 

 sion in which an ocean surmounted by an atmosphere may exist, and 

 in which volcanic fires have not yet become exhausted — that the 

 side of the moon turned towards us is a vast hemispherical mountain- 

 system, rising above the lunar sea-level to a height corresponding 

 to the distance between the Centre of figure and Centre of gravity, 

 or according to some about 30 miles. Is it possible that Vapour 

 from the "ultra-montane " sea may find its way over the border, so 

 as to be converted into snow and ice on the higher lands of the 

 visible hemisphere of the moon ? The mere asking of such a 

 question may subject a writer to a charge of presumption, if not of 

 ignorance, in the present state of astronomical discovery. 



But there is one subject connected with the Geology, or rather 

 Selenology of the moon, on which one may now venture to make 

 suggestions with less hesitation. The theory above noticed 



