296 



in other beds, have probably been drifted there by the action of marine 

 currents. 



It follows from these remarks, that any great change in the mine- 

 ralogical character of a formation must also be accompanied with a 

 corresponding change in the accompanying forms of organic struc- 

 ture once subservient to life. In this way we may explain the great 

 difference between the organic remains of the lower oolitic series of 

 western and central England, and of the contemporaneous coal for- 

 mation on the Yorkshire coast. And in the same way we may also 

 explain an opposite fact, observed more than once by Mr. Murchison 

 and myself during our traverses through the Eastern Alps, that wher- 

 ever a secondary deposit of that great chain approaches the mineral 

 type with which we are familiar in this country, it also contains an 

 imbedded group of organic remains very nearly resembling those we 

 have been taught to regard as characteristic of the formation. 



I believe that the subject to which I am now pointing is one of in- 

 terest and importance ; and I know no one who could do so much 

 justice to it as Mr. Lonsdale, whose admirable knowledge of recent 

 and fossil species, and of the minutest subdivisions of our secondary 

 groups of strata, (strengthened and improved as it is by the perform- 

 ance of the great task he has undertaken so much to the advantage 

 of this Society,) qualifies him to compose an essay which will throw 

 the greatest light upon the physical causes affecting the distribution 

 of organized beings during the long periods of geology. 



In a paper by Mr. Yates, the last I have to notice in connection 

 with our ordinary subjects of discussion, we have a minute detail 

 both of the processes regulating the production of alluvial matter, 

 and of the forms it assumes during its accumulation. He first con- 

 siders the causes of disintegration, independent of the immediate 

 action of running water ; among which he principally enumerates 

 earthquakes, landslips, the various effects of oxidation, and the ex- 

 pansive powers of frost. He then describes the distribution of the 

 comminuted materials by running water, the manner in which they 

 become piled into obtuse cones in passing from lateral to principal 

 valleys, and the various causes modifying the erosive power of rivers. 

 From these subjects he proceeds to the forms assumed by alluvial 

 silt when carried down into standing water, the manner in which 

 lakes become gradually filled up, and the inclination of the stratified 

 masses resulting from the operation. Lastly, he describes the effects 

 produced at the junction of two streams, the depositions on the inter- 

 mediate stagnant points, and the forms of alluvial masses, whether 

 in rivers or lakes, produced by this compound action j and, from the 

 observation of these forms, he draws some practical conclusions re- 

 specting the probable accumulations at the bottom of the sea by the 

 opposition or the union of currents, whether flowing at the same or 

 at different levels. 



Questions of this kind are of most obvious importance ; but they 

 admit of no illustration except by details ill fitted for the nature of 

 this address. I may however, before I finally quit this subject, remind 



