54 



principal Eildons ; to a level in fact within two or three hundred 

 feet of the col or neck which unites them ; but the principal feature 

 which he insists upon is, that the highest summit of the group ap- 

 pears to be composed of a mass of greyvvacke rock, caught up in the 

 midst of the surrounding trap, and so metamorphosed by it as to be 

 with difficulty recognisable ; but the author considers that he has 

 obtained a suite of specimens which leave no doubt as to the fact 

 of the gradation. 



The other important trap- rock is the trap-tufa of Melrose, of 

 which the nature and extent were carefully examined, although the 

 latter is still subject to doubt. The formation appears to commence 

 close to the railway station at Melrose, and to extend in a westerly 

 direction towards Cauldshiels Loch, its breadth being in the Rhy- 

 mer's Glen still considerable, but no section which shews it could be 

 obtained farther west. To the south of the trap-tufa behind Melrose, 

 there occurs a remarkable patch of red sandstone, horizontally de- 

 posited, and evidently identical with that of Dryburgh, where trap- 

 tufa also occurs. There can be little doubt but that the tufa is pos- 

 terior in date to this sandstone, whilst the Eildon porphyry is older. 



A collection of specimens, illustrating the paper, is deposited in 

 the Museum .if the Royal Society. 



2. On cert un Salts of Comenic Acid. By Mr Henry How^. 

 Communicated by Dr Anderson. 



The author commenced his paper with a few observations on the 

 comparative progress of the different departments of organic chemistry, 

 and remarked that the subject of the polybasic acids is not so com- 

 pk'tely studied as could be wished, and that he had chosen his subject 

 for investigation in the hope of adding some information on that point. 



After giving a short history of comenic acid, he pointed out a 

 new method for the purification of the crude acid, which consisted in 

 the use of ammonia as a solvent, in place of potass. In this way 

 he got a salt readily deprived of colour, and whose impure mother 

 liquors were of use in subsequent experiments. 



He then proceeded to detail the salts he had examined. The 

 bicomenate of ammonia, just mentioned, was a salt, crystallizing in 

 beautiful brilliant colourless prisms, whose formula is 



NH^ 0, HO, 0^2 H^ Og + 2 HO. 

 They lose their water of crystallization at 212°. 



