296 Geological Society. 



preciable disturbing forces. Even among the old secondary groups 

 we can sometimes separate littoral formations from those of deep seas, 

 not merely by their mineral structure, but also by their fossils : and 

 in all geological periods of the history of the earth, formations on the 

 shores and formations in deep seas must have gone on together. 



Again, our great formations may be subdivided into many dis- 

 tinct mineralogical groups of strata ; and the large suites of organic 

 remains, characteristic of the formations as a whole, may also be sub- 

 divided into many groups, the species being defined by the mineral 

 structure of the beds to which they are subordinate. 



All this is in harmony with the distribution of the animal kingdom 

 in the existing seas. Some animals may be found almost indifferently 

 on a calcareous, a sandy, or a muddy bottom (for example, the float- 

 ing cephalopodes) ; and the remains of ancient animals of kindred 

 organization occur indifferently in calcareous, siliceous, and argilla- 

 ceous groups of strata. Some animals have lived and propagated 

 under the waters of a muddy shore; the remains of these occur 

 abundantly in our secondary beds of shale. To the very existence of 

 some shells calcareous rocks are necessary ; and on banks of mud or 

 moveable sand, corals and attached zoophytes could find no proper 

 resting place. Hence it is that many species of shells and zoophytes 

 are chiefly characteristic of limestone strata ; and if they exist at all 

 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 j 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 



