Proceedings of the British Association. 355 



reumatical odor which the gas carried up, and which he attribu- 

 ted to an organic cause. To obtain a perfectly pure carbonic 

 acid, for his imitation of the Spas of the continent, he was com- 

 pelled to resort to the pure kinds of marbles. With regard to 

 the presence of organic matter in the subsoil, its detection may 

 be matter of some agricultural interest, when we remember that 

 the small quantities of nitrogen which are required for the growth 

 of those vegetables that first start up in a new country could not 

 have taken place from an accumulation of mould, by the decay 

 of antecedent plants, but must have been derived in a great 

 measure from the animal matter which is contained in the rock 

 upon which they grew, and which proceeds from the exuviae of 

 races of beings belonging to a former period of creation. In a 

 more advanced period of vegetation, this same material may be 

 of some value to the crops that occupy the soil. Dr. D. suggest- 

 ed whether the more compact texture of certain calcareous rocks 

 than of others, might not be connected with the existence in 

 them of organic matter, which by its interposition may prevent 

 a crystalline arrangement of its particles from taking place. It 

 may be that the attraction between the particles of matter, which 

 if uncontrolled, would prove too powerful for the agents of de- 

 composition to overcome, may be weakened by the presence of 

 organic matter, and thus be enabled to supply the vegetables that 

 take root in it with the solid matter which their structure re- 

 quires. To the geologist, too, it cannot but be of interest to 

 trace the several steps by which the organic matter which pri- 

 marily must have constituted so large a portion of the bulk of 

 the various extinct animals and vegetables have disappeared from 

 the strata which enveloped them. 



Mr. Mallet read a paper on the action of Air and Water on 

 Iron. This is the third report for which the Association is in- 

 debted to Mr. Mallet. The object of former tabulated results 

 was to determine the actual loss by corrosion in a given time, 

 and the comparative durability of rust of the principal makes 

 of cast iron of Great Britain, and to discover on what durability 

 depended. The tables of experiments now presented show, that 

 the rate of corrosion is a decreasing one in most cases ; and that 

 the rapidity of the corrosion in cast iron is not so much depen- 

 dent upon the chemical constitution of the metal, as upon its 

 state of crystalline arrangement, and the condition of its consti- 



