54-8 Geological Society : Mr. Lyell on the Recession 



resting on what resembles a sepiostaire. He mentions likewise ten or 

 twelve species of fishes, but without giving names ; also coprolites. 



2. Respecting the form of the mouth of the Ammonites and the 

 changes at different periods of growth, Mr. Pearce states his belief, 

 that the terminal lip or mouth has a different shape in the young 

 shell of almost every species, but assumes in the old a straight out- 

 line, and that he has been aware of this circumstance several years. 

 Of cases of young shells with differently shaped lips, he mentions 

 Ammonites Brongniarti (Inf. oolite), A. sublcevis (Oxf. clay), A. ob- 

 tusus (Lias), A. Kamigii (Kelloway Rock, the mature shell is stated 

 to have a straight mouth), A. Calloviensis (Kelloway Rock, the lip of 

 the old shell is stated to be slightly contracted and to terminate with 

 gently undulating sides), A. Walcottii (Lias), and A. Goodhalli, fur- 

 nished in the mature state with a single horn-like projection at the 

 front of the mouth. In addition to these species he enumerates those 

 noticed in the preceding part of the paper. Mr. Pearce is further of 

 opinion that at different periods of the formation of the shell the la- 

 teral processes were absorbed and reproduced, and that therefore 

 they are found in various stages of growth, but are invariably want- 

 ing in the mature shell. In some species in which the successive 

 mouths were much contracted or expanded, the new shell the author 

 says was continued without the absorption of the lip, leaving a highly 

 projecting rib or a deep furrow*. 



After a careful examination of upwards of twenty species in his 

 collection, with perfect mouths of all ages and from different strata, 

 not including the Oxford clay, Mr. Pearce has found the external 

 chamber to vary considerably in extent, occupying in some speci- 

 mens the whole of the last whorl, but in others less than one-third, 

 and without reference to age or species ; and he therefore suggests 

 that the young animal of the Ammonite filled the whole of the outer 

 chamber, extending also to the extreme points of the lateral pro- 

 cesses in those species which were provided with them ; and thereby 

 not only received support but afforded protection to a portion of the 

 shell extremely liable to injury. In old individuals he is of opinion 

 that the animal when quiescent was entirely contained within the 

 last chamber. 



Jan. 19th. — "A Memoir on the Recession of the Falls of Niagara," 

 by Charles Lyell, Esq., V.P.G.S., was read. 



The general features of the physical geography of the district tra- 

 versed by the Niagara between Lakes Erie and Ontario, Mr. Lyell 

 says, have been described with a considerable approach to accuracy 

 by several writers. Prof. Eaton, in a small work published in 1 824 f, 

 gives a correct section of the formations between Lewistown and 

 the Falls of Niagara, and also refutes the hypothesis of the Lewis- 

 town escarpment being due to a fault by an exposition of the true 



* The author was not acquainted with M. Al. d'Orbigny's work, Pal. 

 Francalse, when he wrote the paper, and was not aware of the views given 

 in it respecting the mouth of the Ammonite. 



f Mr. Lyell's attention was called to this work by Mr. Conrad. 



