NaturaUHistortcal Collections. 145" 



ternal form at the time of its first elevation above the sea — and all the successive 

 disturbing forces which have since acted upon its surface. But none of these 

 elements are constant : no wonder, then, that results derived from distant parts 

 of the earth should be so greatly in conflict with each other. In the formation of 

 valleys there is, therefore, little wisdom in attributing every thing to the action of 

 one modifying cause. We know by direct geological evidence, that nearly all 

 the solid portions of the earth were 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 variations of intensity, that the same formation is in one country hori> 

 zontal, in another vertical ; in one country occupies the plains, in another is only 

 foimd 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 retiring waters of the sea, but a destruction of equilibrium among 

 the waters of inland drainage. Effects like these must have been followed by 

 changes in the channels of rivers, by the bursting of lakes, by great debacles, and 

 in short by all the great phenomena 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 con- 

 dude, 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 par- 

 take of the same complexity of formation. 



The excavation of valleys seems therefore to be a complex result, 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 were formed at the bottom of the sea in times anterior to the elevation of 

 our continents. Such is the great valley of the Caledonian canal, which existed 

 nearly in its present form at a period anterior to the conglomerates 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 valleys 

 of more complex origin ; where the beds through which the waters now pass liave 

 been bent and fractured with an inverted dip at the period of their elevation. Such 

 is the valley of Kingsclere, 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 periods, 

 and to several independent causes. Lastly, we have vaUeys of simple erosion : 

 such are some of the deep gorges and river channels in the high regions of Au- 

 vergne, 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 occupied a large 

 portion of our attention during the past year ; and I may be pardoned for entering 

 a record of my own views on a question of no small complexity, and on which 

 there is still much contrariety of opinion. 



On the Influence of Water on the Respiration of Fishes ; by M. Flouheks. 

 —Water may act on the respiration of fishes chemically, physically, or me- 

 chanically. In a memoir lately read before the Academy of Sciences (12th 

 April,) M. Flourens confined himself to the mechanical influence of water, which 

 has not been heretofore sufficiently attended to. He has observed, that water acts 

 on the branchiae or gills by separating their laminse to facilitate the access of the 

 air ; a result which is founded on numerous experiments. 



It is known that fishes die almost immediately in the air. M. Flourens sup- 

 posed that this arose from a true asphyxia occasioned by the sinking of the 



VOL. II. T 



