Miscellanies. 391 



then crystallization of aqueous vapor actually takes place in the up- 

 per regions of the atmosphere, it is possible that light should be pro- 

 duced. But on the nights of the auroral exhibitions the air is un- 

 usually moist, and from its coolness the line of perpetual congelation 

 is, for the season, unusually low. It is therefore probable that the 

 vapor of the atmosphere is in fact undergoing continual crystalliza- 

 tions as it rises above the line of congelation. Such then is the ori- 

 gin of the light. Other arguments are adduced on this point which 

 we have not now time to mention. Prof. J. next supposes that the 

 molecules of crystals have a peculiar kind of polarity which gov- 

 erns them in their crystalline arrangements. If so, they would be 

 acted on mutually by their own polarities, and also by the magnet- 

 ism of the earth ; and thus would be produced the columns, waving 

 from the unsteady nature of the atmosphere and the continual repro- 

 duction of light from the crystallization of new quantities of vapor. 

 This theory supposes the aurora to be nearer to the earth than 

 facts seem to allow; and on this ground principally rests its improb- 

 ability. It appears however to be deserving of more attention than 

 that which ascribes it to reflections from polar ice, or that attributing 

 it to the existence, in the upper regions, of magnetic particles of 

 that unvaporizable substance, iron. 



10. Third Geological Report to the 'Hist General Assembly of 

 the State of Tennessee, made Oct. 1835. By Prof. G. Troost, 

 M. D. 32 pp. 8vo. Nashville, 1835.— The following passages 

 from this Report contain the result of Prof. Troost's investigations 

 respecting the extent of the coal formations of the State of Ten- 

 nessee. 



" I have ascertained that the places in which coal may be expect- 

 ed, belong exclusively and entirely to that group of mountains 

 which are known by the name of Cumberland Mountain, and are 

 composed of Walden's ridge, Crab-orchard mountain. Brimstone 

 mountain, and some other subordinate ridges of the same system. 



" Commencing with the most southern extremity of our coal- 

 fields, we find that coal first makes its appearance in Mount Sano, 

 east of Huntsville, Alabama, where it crops out in several places. 

 This Mount Sano is a ramification of the Cumberland mountain, 

 which is there divided or terminates in several ridges running gener- 

 ally in a north and south direction. The coal crops out in several 

 of these ridges, which join and form the main Cumberland moun- 



