392 



Geological Society. 



which the trees were discovered. He afterwards applies the phe- 

 nomena which he believes these processes produced to the condition 

 and position of the trees and the arrangement of the surrounding 

 sedimentary matter. The author then enters into the inquiries, 1st, 

 the time which the trees may have required to attain their dimen- 

 sions ; and consequently the minimum of years requisite for the accu- 

 mulation of the vegetable matter; and, 2ndly, what thickness of 

 vegetable matter was necessary to form the stratum of coal nine 

 inches thick, over which the trees stand. Mr. Schomburgk is of 

 opinion that a dicotyledonous tree which would require in temperate 

 climates one hundred years to attain a certain diameter, would arrive 

 at the same dimensions within the tropics in sixty or eighty years. 

 The largest of the fossil trees forming the immediate subject of the 

 paper is equal in circumference to an oak of 130 years growth in 

 this climate, or about 100 for a climate equal in temperature to that 

 of the tropics. Allowing therefore that some time elapsed after the 

 commencement of vegetation on the surface of the then dry land 

 before the trees began to grow, Mr. Bowman infers, that 100 years 

 must be the minimum of time which would be required for the 

 production of the vegetable matter out of which the nine inches of 

 coal were produced. With respect to the depth of the stratum of 

 vegetable matter from which it was formed, Mr. Bowman takes for 

 his data, the thickness of the bed of coal, nine inches ; the distance 

 between the top of the seam and the bottom of the trunk under the 

 arch formed by the roots, fifteen inches ; and for the distance to the 

 surface of the ground, four inches, or in all twenty-eight inches; 

 whereby he infers that the thickness of the solid coal is equal to about 

 one- third that of the vegetable matter out of which it was produced. 



June 10. — A paper was read on the polished and striated surfaces 

 of the rocks which form the beds of Glaciers in the Alps, by Pro- 

 fessor Agassiz. 



This paper was accompanied by a series of plates intended to re- 

 present the effect of glaciers upon the rocks over which they move. 



These effects, consisting of surfaces highly polished, and covered 

 with fine scratches, either in straight lines or curvilinear, according 

 to the direction of the movement of the glacier, are constantly found, 

 not only at the lower extremity, where they are exposed by the 

 melting of the glaciers, but also, wherever the subjacent rock is 

 examined, by descending through deep crevices in the ice. Grains 

 of quartz and other fragments of fallen rocks, which compose the 

 moraines that accompany the glaciers, have afforded the material 

 which, moved by the action of the ice, has produced the polish and 

 scratches on the sides and bottom of the Alpine valleys through which 

 the glaciers are continually, but slowly descending. It is impossible 

 to attribute these effects to causes anterior to the formation of the 

 glacier, as they are constantly present and parallel to the direction of 

 the movement of the ice. They cannot be considered as the effects 

 of an avalanche, for they are often at right angles to the direction in 

 which an avalanche would descend ; they are constantly sharp and 

 fresh beneath existing glaciers, but less distinct on surfaces which 



