Notes on Ammiccm Geology. 237 



One remarkable fact is, that the same day, and about the same 

 time in the day, two other similar whirlwinds were experienced, 

 which moved in nearly parallel lines, one passing through War- 

 wick, Massachusetts, and the other about the same distance to 

 the northeast. They were both less violent ; but one of them 

 at least, the one through Warwick, did considerable damage. 

 The particulars of the other I never had. 



Art. IY. — Notes on A7nenca7i Geology ; by T. A. Conrad. 



Observations on charactei^istic Fossils, and upon a fall of Tem- 

 perature in different geological epochs. 



It has sometimes been objected, that the vahie of organic re- 

 mains, as a basis on which to build the superstructure of geologi- 

 cal science, is lessened by the fact that certain species range 

 throughout different formations ; but these are far from being so 

 numerous as is generally supposed. An instance never occurs in 

 this country, where the species of one formation are continued 

 into an upper one in such numbers as to cause the least perplex- 

 ity or dispute regarding its geological age. All the various eras 

 are admirably recorded, each by its peculiar group of animal or 

 vegetable remains ; and to him who has carefully studied them, 

 they are quite as intelligible as if the hand of nature had arranged 

 them in a cabinet for his use. The few species of a lower, dis- 

 covered among those of an upper group, are not always to be re- 

 garded as contemporary with the latter, as some of them are clearly 

 accidental. Every sedimentary stratum must have been derived 

 from a rock previously formed, and of the first sedimentary rocks, 

 originating in the destruction of primary masses, we, of course, 

 take it for granted that such forms of animal and vegetable life 

 originated in the ocean in which those sedimentary strata were 

 deposited. But when these, disintegrated in their turn, have 

 been, at a more recent period, swept by currents into other seas, 

 we may expect to find occasionally, some few of the species 

 which originally existed, carried with the debris, and thus min- 

 gled with a group very different from that with which they origi- 

 nated. It is true, that in the present state of our knowledge of 



