X80 INTRODUCTION. 



suggestions we have alluded to deserve only the credit 

 "which is due to plausible conjectures./ 



There is, however, a class of minor formations of the 

 tertiary period, in which the testaceous remains point to 

 more certain results. These we have mentioned as de- 

 posited in the beds of lakes. When the body of water 

 from which the deposit in these instances took place was 

 small, it could of course only contain the productions of 

 the lake itself, and of the region immediately around it. 

 Hence species occurring together in such formations 

 must have not only existed contemporaneously, but must 

 have occupied the same geographical region, and have 

 been subjected to the same physical influences. The 

 inferences which may be drawn from them are therefore 

 more to be relied upon. 



Shells of many of the terrestrial species, apparently 

 in a fossilized condition, are often met with in collections, 

 and are said to be brought from the western and south- 

 western parts of the country. They indicate the exist- 

 ence of the most recent tertiary or post tertiary forma- 

 tions, but nothing certain is known of them. Dr. David 

 D. Owen, of New Harmony, Indiana, has discovered an 

 extensive deposit of this kind in Pusey coimty, on the 



1 This view of the subject is strongly corroborated by facts brought to 

 light by the valuable researches of Professor Hitchcock. He has given, to 

 us unequivocal proofs of the existence of birds, in the most ancient mesozoic 

 period, through the evidence of their foot-tracks in the sandstone of the Con- 

 necticut River valley. The number of species he has now made us ac- 

 quainted with is not less than seventy, and yet not a single bone of any one 

 of these has yet been discovered. 



