XC PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



river mouths. Another result is that in all the formations of the 

 world, in the air, on land, and in or under the water, only six great 

 classes of microscopic forms are to be found. These are, 1. Siliceous, 

 of which there are four classes, viz. Polygastrica, Polycystinise, 

 Phytolithariee, and Geolithise, and 2. Calcareous, of which there are 

 two classes, viz. Polythalamise and Zoolitharise. But I must refer 

 you to the work itself for the further distribution of these classes, 

 where each preponderates, and how certain forms serve in many cases 

 to designate one formation or another. The work is illustrated by 

 forty-one plates, executed with great ability. I will only mention 

 that the separate results of the analytical examinations of the 836 

 substances are given in this work, and that in most cases the author 

 appears to have made from five to ten analyses of each. These are 

 generally arranged geographically in the first instance, and the results 

 of the general examination of each district are separately given. 



I may also mention that a second edition of Bernhard Cotta's 

 agreeable and instructive work entitled * Geologische Bilder,' Geolo- 

 gical Pictures, has appeared during the last year. 



The French * Bulletin' for the last year contains several interesting 

 papers bearing on the application of Chemistry to Geology. A paper 

 by M. Delesse (Bull. p. 127), entitled, *'0n the action of alkalies on 

 rocks," points to the fact that as silica in a soluble state is now found 

 in a great number of sedimentary rocks, and as, equally, the alkalies or 

 the alkaline salts exist in small quantities in almost all spring waters, 

 the action of the latter on the former, " although feeble, having been 

 continued throughout all geological time, has necessarily contributed 

 powerfully to the formation of pseudomorphisms" (p. 141). Granite 

 and quartzose porphyry are but slightly attacked by alkaline solu- 

 tions. Lava, basalt, melaphyre lose under 20 per cent, by their 

 action. Trachyte, retinite, perlite, and obsidian are the rocks which 

 are the most readily attacked, losing sometimes to the extent of 40 

 per cent. Further, decomposed rocks are much more readily acted 

 upon than the same rock when undecomposed. " Cceteris jjaribus, 

 the action of alkalies on rocks is the greater according as the rocks 

 are richer in silica, less crystalline in structure, or contain less hyaline 

 quartz" (p. 140). As bearing on this sam^e subject, some observa- 

 tions by M. Saemann (p. 143) are also interesting. 



M. Delanoiie (p. 562) suggests several very necessary cautions in 

 the application of the theory of metamorphism. He is willing to 

 admit to their full extent the important influence of heat and gaseous 

 emanations in rocks, but not the intrusion throughout entire masses 

 of substances entirely foreign to the composition of those rocks. He 

 contests the possibility of dolomitization by metamorphic action, also 

 the introduction of felspar into rock-masses by the same action, 

 contending in either case that the chemical elements necessary for 

 the change pre-existed in the rocks, and that they have only been 

 modified by heat. M. Delanoiie contests (p. 569) also some expla- 

 nations that had been brought before the Society by MM. Delesse, 

 Deville, and Durocher, accounting for the presence of sulphur in 

 thermal waters, and passes in review the various changes brought 

 about by the percolation of rain-water through the earth. 



