CXll PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



At the same time there are phsenomena which even this theory 

 fails to explain satisfactorily, and we shall probably not greatly err if 

 we assume that, while the chief amount of altitude is due to the 

 accumulation of ejected matter round the orifice, a certain amount of 

 paroxysmal elevation has taken place, although not sufficient to 

 support the entire theory of the late Leopold von Buch. 



I may also mention that this work contains much additional infor- 

 mation respecting the tertiary deposits of Germany and the age of 

 the associated brown-coals. 



Prof. Ehrenberg continues his investigations respectmg the Infu- 

 soria with his wonted energy. Interesting notices of his discoveries, 

 and his communications thereon, will be found in Leonhard and 

 Bronn's Jahrbuch for the past year. The remains of many forms 

 of Polythalamia have been found by the Professor in the green sands 

 of various formations, some of which are so well preserved that they 

 have led to interesting physiological discoveries. 



A question of great interest, both to zoologists and to geologists, 

 has recently attracted the attention of the Geological Society of 

 France and of the Academy of Sciences. The habit of several spe- 

 cies of zoophytes and mollusca to perforate rocks of different kinds is 

 one which has not yet received a satisfactory solution. Whether 

 this result is produced by chemical or mechanical means has not yet 

 been fully proved, although the balance of evidence seems now lean- 

 ing towards a m.echanical solution. In this state of the question, and 

 while many persons are still disposed to believe that these perforations 

 have been produced by other means, the statements lately made in 

 Paris, and the specimens laid before the Institute and the Geological 

 Society, are sufficiently interesting to merit notice on the present 

 occasion. It was originally supposed that calcareous rocks alone had 

 been perforated by these animals, but the same phsenomena have 

 recently been observed in other rocks. M. Caillaud of Nantes has 

 found the granite of Poulinguen, in the Bay of Croisie, perforated by 

 Pholades. In this case, the striae in the hollows corresponded with 

 the spinous processes of the shells, and left no doubt that the effect 

 was here at least due to mechanical action. Here, however, the 

 decomposed state of the granite may have facilitated the operation. 



At a more recent period, M. Eugene Robert exhibited a block of 

 Silurian sandstone, belonging to the transition formation which 

 forms the shore of the great bay of Douarnenez, perforated by nume- 

 rous holes made by Echini living in them. Each circular cavity was 

 exactly proportionate, both in size and shape, to the Echinoderm 

 in it. 



Prof. Long, of Grenoble, well known for his many able geological 

 memoirs, has recently requested M. Valenciennes to lay before the 

 Academy of Sciences several specimens of perforating Echini which 

 have established themselves in the granite of Guerande, in the Bay of 

 Croisie, near Turballe, not far from Piriac. This granite is similar 

 to, and in the same state of decomposition as, that of Poulinguen, 

 and is perforated over a space of several kilometres by JMollusks and 

 Echinoderms, and the Echini are evidently of the same species as 



