Ixxvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



of felspar crystals through a sediment derived from showers of vol- 

 canic ash, constituting thus a rock of which numerous instances are 

 familiar to the explorers of our palaeozoic districts. 



The line of research chosen hy M. Delesse in the papers just no- 

 ticed, and many others from his pen, is one sure to be productive of 

 valuable results. The mineralogy of rock masses is of great conse- 

 quence to the geologist, but to he satisfactorily treated must be dealt 

 with by inquirers who are, like the author cited, practical geologists, 

 and ready at the same time to avail themselves fully of the aid of 

 chemistry. The treatment of the majority of simple minerals fails, 

 in the main, within the sphere of the chemist ; so much so, that we 

 might almost be warranted in regarding mineralogy as the palseonto- 

 logy of chemistry. 



Among the "general observations" prefixed to the new volume of 

 M. D'Archiac's History are some brief but profound remarks on pe- 

 trographical changes, and on the distinctions between the greater 

 metamorphism of sedimentary formations and the lesser or metamor- 

 phism of contact, the latter being dependent on the action of igneous 

 causes. The author calls attention to the fact of consolidation and 

 tendency to metamorphism in the sedimentary strata of mountain 

 masses, exhibited by the hardening of the limestones, their tendency 

 to assume certain peculiarities of colour and frequently subcrystalline 

 and even saccharoid textures, the conversion of the marls and sandy 

 clays into schistose beds, and the indurated and compact characters 

 of the sandy elements. On the other hand, the continuations of the 

 same beds, when forming horizontal table-lands or extended plains, 

 composed of conformable and undisturbed strata, exhibit entirely 

 distinct mineral characters, being comparatively unsolidified and put- 

 ting on very difFerent features of colour and texture. These differ- 

 ences between the same set of rocks — in the one case disturbed, 

 crumpled up and contorted, in the other resting almost in their ori- 

 ginal repose — are exhibited by formations of all ages indifferently, 

 and would lead to the inference that the greater metamorphism is 

 mainly due to energy of dynamical causes. 



Although properly the subject should be mentioned under a distinct 

 head, I may here allude to Mr. Tylor's interesting essay on the changes 

 of sea-level effected by existing physical causes during stated periods 

 of time, a paper abounding in suggestions of general interest and in 

 curious calculations. As the author continues to pursue the same 

 line of inquiry, it would be premature to discuss his conclusions 

 now. 



Still more distinct and far less practical in its theme is Mr. Saull's 

 pamphlet treating of the connexion of geological phsenomeua with 

 astronomical causes. 



Text-books. 



The spread of a love for geology among the people and students of 

 science has its svirest indication in the appreciation of text-books and 

 synoptical treatises. The year 1853 has not been behind in affording 

 evidences of the popular appreciation of our science. That great 



