1 38 Geological Society. 



filled up with transported matter, and afterwards been excavated a 

 second time, — generally to a depth below their original bottom. 



6. The autliors conceive, with the writers already mentioned, 

 that a satisfactory explanation of these phenomena may be derived 

 from the effects of the latest volcanic eruptions of Central France. 

 For the more recent lavas appear to have dammed up the channels 

 of several rivers, and converted ancient valleys into lakes ; wherein, 

 as at Aidat and Chambon, alluvial matter is continually accumulating 

 at present. The modern lava of Montpezat, in the \'ivarrais, has 

 thus obstructed the course of the Fontaulier, and given origin to a 

 lake, since filled with river alluvion and volcanic ashes; and these 

 deposits themselves, together with a part of the volcanic barrier, 

 have been subsequently cut through by the action of the river and 

 the waters of the lake. The early and more co])ious lava-currents 

 of Auvergne must have occasioned larger lakes than those of recent 

 periods ; and these, as has been stated by other authors, seem to 

 have been gradually filled up with materials introduced by rivers, 

 and occasionally by floods, from the sides or craters of volcanoes, 

 probably during their moments of eruption ; through which accu- 

 mulations new valleys were excavated by the continued action of 

 the rivers : — as at Mont Perrier, to about 100 feet ; and at Maurice 

 on the Allier, to the depth of 400 feet below their original bottoms. 

 The high antiquity of these alluvial depositions is inferred from the 

 fact, that their lowest remnants occupy as elevated a position on the 

 sides of the valleys, as the lava-currents of intermediate age in Au- 

 vergne, and from the compactness and enormous mass of the tra- 

 chytic breccias, which overlie and alternate with the alluvions. 



7. Lastly, since the sand and gravel containing the fossil bones 

 found on two different sides of the mountain of Perrier are overlaid 

 by a vast mass of trachytic breccia, it is concluded, that the ele- 

 phant, rhinoceros, hippopotamus, hysena, tiger, wild cat and other 

 quadrupeds, whose remains have been recently disinterred, must 

 have been inhabitants of this district before the most recent cones 

 and lavas of Auvergne had appeared, or the valleys had been exca- 

 vated to their present depth ; and even before the fires of Mont 

 Dor were extinguished. 



Jan. 2, 1829. — A letter was read, addressed to R. I. Murchison, 

 Esq. For. Sec. G.S. &c. by G. W. Featherstonhaugh, Esq. F.G.S. 

 " On the Series of Rocks in the United States." 



Mr. Eaton has published in Silliman's Journal of Science, vol. xiv. 

 a Synopsis of the rocks of North America. In the commencement of 

 the present paper, the author, after having made himself acquainted 

 by personal observation with the rocks of England, — states his opi- 

 nion that the rocks in North America, which would appear from Mr. 

 Eaton's Synopsis to succeed one another in an order perfectly irre- 

 concileable with that which has been observed in the British Islands, 

 do in reality follow the same order. 



A comparative view of the respective systems of Mr. Eaton and 

 the author of this letter will be conveyed in the following table : — 



Series of North American Rocks, 

 (According to Mr. Eaton.) (Mr. Featherstonehaugh.) 



Superficial Analluvion. 



