380 



elusive proof of an alternate rising and sinking of the same land since 

 this region was inhabited by man, first a depression of the ground 

 of at least 50 feet below its former level, and then a re-elevation of 

 the same amounting to at least 50 feet. 



The probable cause of the prolonged and insensible movements 

 of large masses of land opens a wide and inviting field for specu- 

 lation. As we know that volcanic action is never dormant in some 

 parts of the interior of the globe, it seems most natural to imagine 

 that an alternate expansion and contraction of the earth's crust may 

 arise from a gradual increase or diminution of its temperature. 

 Mr. Babbage has suggested that as many common kinds of stone 

 have been shown by experiment to augment in volume when heated, 

 and decrease in bulk when slowly cooled, a great thickness of sub- 

 jacent rock may cause the surface to rise or sink according to the 

 variations experienced in the subterranean temperature. We have 

 also to consider the eflfects which might result from the slow cool- 

 ing and crystalh'zation of large reservoirs of melted matter, on 

 which subject we have unfortunately as yet few experiments to 

 guide our conjectures. We know not, for example, whether the 

 passage from a fluid to a solid state would uplift or let down an 

 incumbent mass of rock. A dense fluid, subjected to immense 

 pressure, may, perhaps, on crystallizing into a rock like granite, oc- 

 cupy more space in its state of solidity. I need not remind you 

 that as ice floats in water, so a bar of cast iron floats on the surface 

 of melted iron. 



But however obscure the origin of the movements in question, 

 their reality if admitted affords a key to the interpretation of a va- 

 riety of geological appearances, some of which I shall now proceed 

 to consider. 



Dr. Beck has mentioned that the oldest strata in Denmark are 

 often covered by deposits of gravel, sand, and loam, several hun- 

 dred feet thick, in which, but more commonly upon them, lie erratic 

 blocks. The sand and gravel beds rarely contain any fossils, but 

 "when shells do occur they are absolutely identical with living species. 

 He has also found, in the lower valleys of Jutland, more than se- 

 venty species of shells now living in the German Ocean. These 

 facts agree precisely with others which I observed in different parts 

 of Sweden, and which I have described in the memoir before al- 

 luded to. On the west coast, between Uddevalla and Gothenborg, 

 the beds of sand, gravel, and clay, containing recent oceanic shells, 

 are seen at various heights from 100 to 300 feet above the sea. 

 M. Alex. Brongniart formerly pointed out those which rest on the 

 gneiss, near Uddevalla, and like him I saw Balani still attached to 

 the rocks at the height of more than 150 feet above the sea-level. 

 I ought, however, to state that at the points where I discovered 

 them they had not been exposed to decomposition in the atmosphere 

 ever since their emergence. On the contrary, the adhering shells 

 had been protected by a covering of shelly sand only removed of 

 late years for road-making. I need scarcely insist upon the obvious 

 inference that the Balani and corallines which also cover the rocks, and 



