844 LECTURES ON GEOLOGY. 



trees, and bones of the mammoth, or fossil elephant, not petrified, 

 found in Siberia, fully confirm this opinion of the heat of these 

 climates being greater immediately previous to the deluge. 



We have remarked that all the strata, except the primary, and 

 we may add the trap rocks, are evidently of sedimentary origin j 

 but as we have no reason to suppose that the quantity of water 

 covering the earth has ever varied in any great degree, how are we 

 to account for this conversion of sea into dry land ? A considera- 

 tion of the changes still going on upon the earth's surface will 

 afford us a satisfactory solution of this most interesting problem. 

 The agents employed in producing these changes are the antago- 

 nizing powers of fire and water ; the former by means of volcanoes 

 and earthquakes adding to continents, and raising islands from the 

 bottom of the ocean j the latter in the form of rain and torrents, 

 levelling uplands, and excavating vallies, and more rapidly wearing 

 away our coasts by the billows which unceasingly break upon 

 them. 



We will just mention a few instances of these phenomena, of 

 recent occurrence. The morning after a tremendous earthquake, 

 at Valparaiso, in 1822, the whole line of coast, to the distance of 

 100 miles from north to south, was found to have been raised 

 several feet above its former level ; and Mrs. Graham remarked 

 that this was only one of a series of elevating convulsions, from 

 observing several ancient lines of beach covered with shells and 

 shingle full fifty feet above the present level of the sea. The 

 number of islands raised from the sea within the historic period is 

 very great -, the last instance of the kind occurred off the coast of 

 Sicily, but this island has been again reclaim.ed under the dominion 

 of Neptune, and only exists as a shoal. The above-mentioned 

 elevations of land took place suddenly, but the shores of the Baltic 

 are now pretty clearly ascertained to have been gradually increasing 

 in height for more than a century. 



An idea of the destructive effects of running water upon our 

 continents may be formed from the quantity of solid matter carried 

 down annually into the sea by the Ganges, which is estimated to 

 exceed a mass twelve times the size of the great pyramid, the 

 height of which is 500 feet, and the base of which covers eleven 

 acres. Although the ravages of the sea upon our coasts are very 

 much influenced by local causes, they are almost universal in their 

 occurrence j for the exceptions are not real, and where we find the 

 sea retiring as it were, it is merely depositing in some bay or 

 recess, the debris it has washed from the neighbouring promonto- 

 ries. The present rate of encroachment on the Yorkshire coast is 

 about four yards annually ; and at Sherringham, in Norfolk, the 

 flag staff has been thrice removed inland within the last fifteen 

 years, in consequence of the advance of the sea. The sand and 

 mud being carried round the projecting part of the Norfolk coast 

 is deposited at the mouth of the river Yare, where thousands of 

 acres are reclaimed, again to be submerged whenever their protect- 

 ing cause is removed. 



