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In accordance with the important fact ascertained by 

 Mr. William Smith, of peculiar fossils being found in 

 and characterizing particular strata, the fossil shells in 

 the succeeding table are arranged in the order of the 

 strata in which they occur, commencing with the ear- 

 liest. Each genus is placed under the formation in 

 which it is first found; and each succeeding stratum is 

 marked, in which the several species are discovered. 

 But as, previously to Mr. Smith's " Strata identified by 

 Organized Fossils," and Mr. Sowerby's " Mineral Con- 

 chology," with " an arrangement of strata, shells, and 

 places," by Mr. Farey, contained in the last mentioned 

 work, no publication has regularly particularized the 

 strata in which the described fossils have been fonnd, I 

 have availed myself of the information yielded by Mr. 

 Sowerby's work for the facts which the table contains. 

 It is however proper to observe, that, in the present 

 state of our knowledge, this table must necessarily be 

 far from perfect. Many shells must exist in the different 

 strata, of species, and even of genera, which have not yet 

 been noticed; and various circumstances may have led 

 to erroneous conclusions : but, notwithstanding this, it is 

 hoped, that sufficient will be rendered evident by it to 

 establish the important and valuable facts stated by 

 Mr. Smith, and to assist the student in this part of his 

 inquiries. 



It is presumed also, that, by pursuing this mode of 

 arrangement, we may assist and correct our conjectures, 

 whilst contemplating the relative periods of the crea- 

 tion, duration, and extinction of the animals, which are 

 only known to us through their mineralized or otherwise 

 preserved fossil remains. To obtain complete information 

 on these points may be impossible, but every approximation 

 must be accompanied by interesting instruction. 



