294r Geological Society. 



fying cause. We know by direct geological evidence, that nearly 

 all the solid portions of the earth vvere once under the sea, and 

 were lifted to their present elevation, not at one time, but during 

 many distinct periods. We know that elevating forces have not 

 only acted in different places at different times, but with such va- 

 riations of intensity, that the same formation is in one country ho- 

 rizontal, in another vertical ; in one country occupies the plains, in 

 another is only found at the tops of the highest mountains. Now 

 every great irregular elevation of the land (independently of all 

 other results) must have produced, not merely a rush of the re- 

 tiring waters of the sea, but a destruction of equilibrium among the 

 waters of inland drainage. Effects like these must have been fol- 

 lowed by changes in the channels of rivers, by the bursting of 

 lakes, bj' great debacles, and in short by all the great phsenomena 

 of denudation. In comparing distant parts of the earth, we may 

 therefore affirm that the periods of denudation do not belong to 

 one, but to many successive epochs. And by parity of reasoning 

 we may conclude that the great masses of incoherent matter which 

 lie scattered over so many parts of the surface of the earth, belong 

 also to successive epochs, and partake of the same complexity of 

 formation. 



The excavation of valleys seems therefore to be a complex re- 

 sult, depending upon all the forces, which, acting on the surface of 

 the earth, since it rose above the waters, have fashioned it into its 

 present form. We have old oceanic valleys which vvere formed at 

 the bottom of the sea in times anterior to the elevation of our con- 

 tinents. Such is the great valley of the Caledonian canal, which 

 existed nearly in its present form at a period anterior to the con- 

 glomerates of the old red sandstone. We have longitudinal valleys 

 formed along the line of junction of two contiguous formations, 

 simply by the elevation of their beds. To this class belong some 

 of the great longitudinal valleys of the Alps. We have other val- 

 leys of more complex origin; where the beds through which the 

 waters now pass have been bent and fractured with an inverted 

 dip at the period of their elevation. Such is the valley of Kings- 

 clere, described in a former volume by Dr. Buckland. We have 

 valleys of disruption, marking the direction of cracks and fissures, 

 produced by great upheaving forces. Such are some of the great 

 transverse valleys of the Alps. Of valleys of denudation our island 

 offers a countless number. Some are of simple origin : for example, 

 the dry combes and valleys of the chalk, which appear to have 

 been swept out by one flood of retiring waters during some period of 

 elevation. Others are of complex origin, and are referrible to many 

 ))eriods, and to several independent causes. Lastly, we have valleys 

 of simple erosion : such are some of the deep gorges and river chan- 

 nels in the high regions of Auvergne, excavated solely by the long 

 continued attrition of the rivers which still flow through them. 



I should not have dwelt so long upon this subject, had it not occu- 

 pied a large portion of our attention during the past year; and 1 



may 



