THE FORMATION OF COAL. 135 



considerable quantity of earth and stones adhering to their 

 roots : this explains the upright position of the trees in the 

 lake. 



Such trees falling into water of sufficient depth to enable 

 them to turn over must sink root downward, or float in an 

 upright position, according to the quantity of adhering soil. 

 The difference of depth would tend to a more rapid penetration 

 of water in the lower parts, where the pressure would be 

 greatest, and thus the upright or oblique position of many of 

 the floating trunks would be maintained till they absorbed 

 sufficient water to sink altogether. 



It is generally assumed that fossil trees which are found in 

 an upright position have grown on the spot where they are 

 found. The facts I have stated show that this inference is by 

 no means necessary, not even when the roots are attached and 

 some soil is found among them. In order to account for the 

 other surroundings of these fossil trees a very violent hypoth- 

 esis is commonly made viz. that the soil on which they grew 

 sunk down some hundreds of feet without disturbing them. 

 This demands a great strain upon the scientific imagination, 

 even in reference to the few cases where the trees stand per- 

 pendicular. As the majority slope considerably the difficulty 

 is still greater. I shall presently show how trees like those 

 immersed in Aachensee may have become, and are now becom- 

 ing, imbedded in rocks similar to those of the Coal Measures. 



In the course of subsequent excursions on the fiords of 

 Norway I was reminded of the sub-aqueous forests of the 

 Aachensee, and of the paper which I read at the British Asso- 

 ciation meeting of 1865, of which the above is an abstract 

 not by again seeing such a deposit under water, for none of 

 the fiords approach the singular transparency of the lake, but 

 by a repetition on a far larger scale of the downward strips of 

 denuded forest-ground. Here in Norway their magnitude 

 justifies me in describing them as vegetable avalanches. They 

 may be seen on the Sognefjord, and especially on those 

 terminal branches of this great estuary, of which the steep slopes 

 are well wooded. But the most remarkable display that I have 

 seen was in the course of the magnificent, and now easily made, 

 journey up the Storfjord and its extension and branches, the 

 Slyngsfjord, Sunelvsfjord, Nodalsfjord, and Geirangerfjord. 

 Here these avalanches of trees, with their accompaniment of 

 fragments of rock, are of such frequent occurrence that sites of 

 the farm-houses are commonly selected with reference to possi- 



