Geological Society. 5 1 5 



has hitherto been known beyond the fact that all its shores and its 

 general aspect are volcanic ; Mr. Smith has at length discovered 

 sections at the elevation of about 2000 feet, in the central part of 

 the island, which exhibit compact limestone, containing fossil re- 

 mains of Conus and many other shells of the tertiaiy period. No- 

 thing is visible beneath this limestone, but above it are lofty preci- 

 pices which exhibit several beds of sub-aerial lava, lapilli and ashes, 

 alternating with beds of soil converted to brick by the beds of lava 

 incumbent on them. In some of these volcanic beds of loose tex- 

 ture, there occur abundant remains of small roots of trees converted 

 to carbonate of lime, in which few traces of structure have been 

 preserved. I have occasionally seen similar remains of roots, in a 

 state of lac lunse, in loose calcareous sand, and gravel-beds in En- 

 gland, e.g. in the coralline gravel of the lower greensand formation 

 at Coxwell, near Faringdon, and in a diluvial sand and gravel-pit 

 near Claydon in Buckinghamshire. 



GEOLOGICAL DYNAMICS. GLACIAL THEORY. 



Daring the last year M. Agassiz has introduced a new and power- 

 ful machinery into the Dynamics of Geology, by asserting the 

 claims of ice to be admitted to the list of locomotive forces that 

 have operated largely not only in forming morains (i. e. mounds and 

 ridges of gravel and clay intermixed with large fragments of rocks) 

 on the flanks and at the lower extremity of existing glaciers, but 

 also in transporting erratic blocks with the detritus of morains to 

 distant regions, and re-arranging them by the force of floods that 

 originated in the melting of ice and snow. 



In the month of June ISiO, a notice was read to us by hiin on 

 the polished and striated surfaces of rocks in the beds of glaciers in 

 the Alps ; and another notice in the following November, on the 

 evidence of the existence of glaciers in Scotland, Ireland, and En- 

 gland. In the summer of 1840 he published in Switzerland, in his 

 ' Etudes sur les Glaciers,' a description of facts which lie at the 

 foundation of this question, illustrated by a splendid series of plates> 

 representing the actual condition and residuary eff'ects of existing 

 glaciers in the Alps. These phtenomena are so essentially prelimi- 

 nary to the investigation of the evidences of ancient glaciers in 

 regions where they are now unknown, that no man is fully quali- 

 fied to enter upon this question who has not prejiared himself by 

 the study of modern glaciers with a special view to their residuary 

 pIusHomena, which have been overlooked, or referred to other causes 

 by preceding observers in Alpine regions. 



After due acknowledgment of the discoveries of Scheuchzer, Gru- 

 ner, De Saussure, Hugi, Venetz, and Charpenticr, M. Agassiz exa- 

 mines the origin of glaciers in the transformation of snow into solid 

 ice, the different conditions of tiiis ice in its \'arious stages of ad- 

 vancement, the causes of its movement, tlie history of the detritus 

 that falls upon it and is transported along its surface and lodged in 

 the form of morains upon its sides and at its lower extremity, and 

 the modifications of these morains by the waters of temporary ponds 

 2 M 2 



