10 (GEOLOGICAL MEMOIRS. 



St. Eranchy the amount is 0-12, and in two decomposed granites 

 only 0-04 and 0-03 ; thus showing that where granite is decomposed 

 into sand and clay, instead of the amount of azote being increased, 

 it is very considerably diminished. Also where granite passes into 

 trachyte, as at Sandy Braes, near Antrim, the amount is reduced to 

 a mere trace. Diorite, malaphyr, euphotide, serpentine, and espe- 

 ,cially variolite, also contain a well-marked quantity of organic mat- 

 ters. Trachyte and phonolite contain only a small quantity ; but 

 pitchstone and obsidian sometimes a considerable amount, as in the 

 case of the beautiful black obsidian from Iceland, which contains as 

 much as 0-15, imparting to it its black colour. This is expelled by 

 the application of heat, and we can thus explain why it then becomes 

 white or grey, and passes into pumice. Therefore, although pitch- 

 stone and obsidian are looked upon as volcanic glasses, they have 

 been produced not only in the presence of water, but also of organic 

 matter, and thus not by mere igneous action. Azote is also found 

 in anhydrous lavas, but in such very small quantities that it may 

 have been introduced since the formation of the rock, by atmospheric 

 agencies. In hydrous basalts and traps the quantity is much more 

 considerable, and sometimes amounts to as much as 0-30. However, 

 it is an important fact in connexion with the existence of organic 

 matter in igneous rocks, that meteoric stones occasionally contain a 

 very considerable amount of carbonaceous matter, and even some 

 azote ; and, with reference to this, the author says that it is easy to 

 jconceive that organic matters may be formed directly and completely 

 by the combination of their elements. The remarkable experiments 

 of Berthelot {' Chimie Organique fondee sur la Synthese,' 1860) 

 prove indeed that, for a large number of them, this synthesis is pos- 

 sible in the laboratory. Accordingly, the organic matters in meteoric 

 stones do not warrant the conclusions of those who have argued that 

 they come from regions inhabited by living beings. We must, how- 

 ever, at the same time bear in mind that, as shown by the author, 

 subterranean water contains organic matter, and it may thus have 

 been introduced into minerals and rocks formed in its presence or by 

 its action. 



The various stratified rocks are those considered in detail, and the 

 author shows that they usually contain a well-marked amount of 

 azote ; and this is especially the case with those of an argillaceous 

 nature, which appears to have a great affinity for organic matter, 

 and to retain it with great persistence. Of course, in the case of most 

 stratified rocks, one may very safely conclude that the minute ani- 

 mals and plants, or fragments of larger organisms, mixed up with 

 the mud at the time of deposition have furnished the organic com- 

 pounds which have been shut up and retained to the present period ; 

 and in order to illustrate this, the author, in a special division of his 

 memoir, treats on the amount of azote in recent stratified deposits, 

 including alluvia, soils, and water. As an important fact in con- 

 nexion with the subject, he shows that, although there may have 

 been an immense excess of organic matters present, yet only a com- 

 paratively small amount is permanently retained ; that derived from, 



