Hints on the Iceberg Theory of Drift. 1 69 



acid, much diluted, had the following reactions: With sulphuric 

 acid, a white precipitate, which redissolves in an excess of the 

 precipitant. Nitrate of potash, no change of appearance. Sul- 

 phate of ammonia, a white precipitate, soluble in acids. Sulphate 

 of soda, the same ; the precipitate is less soluble. Nitrate of soda, 

 no change apparent. 



The most remarkable action follows the addition of sulphate 

 of potash. A solution containing only a minute quantity of this 

 salt, annihilates as it were the A state of the columbic acid, and 

 changes it to its ordinary state. At the instant of acquiring its 

 usual acid relation to the substances present, it precipitates and 

 carries down with it some portion of them in an insoluble state. 

 If a solution of columbic acid in its A state, be boiled in a flint 

 glass vessel, and afterwards a drop of sulphuric acid or a sulphate 

 is added, a precipitate denoting the presence of sulphate of potash 

 falls. When the columbic acid has been prepared by heating a 

 native compound, with 6 or 8 parts of bisulphate of potash, it 

 always contains sulphuric acid. A quantity of bisulphate equal 

 to 12 or 15 times the weight of the mineral being used, the acid 

 is readily obtained pure. 



Art. XXI. — Hints on the Iceberg Theory of Drift ; — in a letter 

 from Mr. Peter Dobson to Prof. Edward Hitchcock. 



Extract of a Letter from Prof. Hitchcock. 



Messrs. Editors, — You will recollect that in Mr. Murchison's 

 Anniversary Address before the London Geological Society, for 

 1842, he gives credit to Mr. Peter Dobson of Yernon in Connec- 

 ticut, as "the original author of the best glacial theory;"* and in 

 proof quotes a paper by Mr. Dobson in the Journal of Science for 

 1826. In looking over my papers lately, I found a letter from 

 Mr. Dobson on this subject, written six years ago, which I send 

 you, in the hope that you will publish it; because it carries out 

 his views more minutely than does the paper referred to by Mr. 

 Mnrchison ; and these views are with him evidently original. I 

 am the more inclined to do this, as I fear, from not finding any 



* See this Journal, Vol. xliii, p. 200. 

 Vol. xlvi, No. 1.— Oct.-Dec. 1843. 22 



