Freshwater Limestone in Forfarshire, ^c. 95 



Appendix II. 



I am indebted to Mr. Faraday,, P.R. and G. S.S.j of the Roysl Institution, 

 for an examination of different specimens of marl, limestone, &c., which ori- 

 ginated in a desire to ascertain whether the marl afforded any traces of animal 

 matter. It appears from this examination, that the test applied is so exceed- 

 ingly sensible to the smallest traces of ammonia ; and that these traces may be 

 communicated to the specimen under trial by causes so slight, that the indica- 

 tions given by the test of the presence of ammonia afford but equivocal proof 

 that animal matter existed originally in the specimen. This being the case, 

 although all the marls from the Bakie, &c. gave, when tried, unequivocal signs 

 of the presence of ammonia, I have omitted any mention of that circumstance 

 in the text. 



The following, as Mr. Faraday informs me, was the test employed. " The 

 marl was heated in a glass tube to a red heat, upon which it gave out the 

 smell peculiar to burnt animal matter. Turmeric paper, upon being brought 

 near it, was tinged of a reddish brown colour, indicating the presence of am- 

 monia; the tint disappearing upon the application of a moderate temperature. 



" The delicacy of this test is such, that it is necessary, not only that the glass 

 tube should be previously examined, but that the specimen should be fresh 

 from the centre of a mass and not handled. The importance of such attention 

 will be shown by the following experiment. 



"Some sea-sand was heated in a crucible to red heat for half an hour, and 

 then poured out on a copper plate and left to cool. A portion of it was then 

 introduced into a glass tube by a platina spoon, and it caused no change of 

 colour in the turmeric paper ; but another portion of the sand which had been 

 heated, upon being poured into the palm of the hand, turned over several 

 times by the finger and then examined in the same manner, gave decided 

 traces of ammonia. It may be interesting to enumerate the different sub- 

 stances, which when examined with due attention to the circumstances above 

 stated, gave indications of ammonia. The result will serve as a caution against 

 founding any theory on the presence of that alkali, except when it is very 

 abundant." 



1. Loose calcareous marl, from the Upper Freshwater formation. Isle of Wight . , . . slight 



indications. 



2. Limestone of the Lower Freshwater formation, White-cliff Bay, Isle of Wight . . slight. 



3. Gypsum, from Gypse a ossemens. Trielle, in the Paris Basin . . plentiful, zeith smell of 



fetid limestone. 



4. Bone of quadruped, from ditto . . afforded no indications of ammonia, but the smell of 



burnt animal matter. 



