On the Natural History of North America. 211 



to suppose. The general range of these American moun- 

 tains is north-east and south-west. In some places the 

 north-west and in others the south-east sides are the 

 steepest. The valley which is comprehended between the 

 North Mountains and the Blue Ridge is principally calca- 

 reous. Very generally the veins of limestone run parallel 

 with the mountains, that is, north-east and south-west. 

 When the nearest mountain varies from this direction, I 

 observed that the adjacent strata in the valley do the same. 

 These strata are sometimes perpendicular in their position, 

 but never horizontal. It is remarkable, however, that most 

 of the strata in the country west of the great Alleghaney 

 mountains (which are to the west of the North Mountains) 

 are arranged horizontally. This observation applies to the 

 strata of limestone, schistus, freestone, and even to the 

 stone coal and iron ore. This difference in the disposition 

 of the strata east and west of the Alleghaney mountains is 

 well entitled to the attention of naturalists. I have made 

 it the subject of an express memoir. 



It has long been conjectured that the calcareous valley 

 which I have mentioned was once an arm of the ocean. 

 This opinion has been maintained by Mr. Jefferson in his 

 Notes on the State of Virginia. I entertain no doubt as to 

 the antient covering of this valley by the sea, especially 

 since my late researches have convinced me that the calca- 

 reous strata abound with marine exuviae of various kinds. 

 It is a circumstance very remarkable, that marine vestiges 

 are much less abundant in the calcareous strata that are 

 nearest to the present ocean, than in those which are at a 

 much greater distance from it. Thus, although immense 

 quarries of marble have been opened in the neighbourhood 

 of Philadelphia, I have never yet been able to discover, 

 though I have for several years been in search of them, 

 the most distant semblance of a shell, or any thing of the 

 kind, in hundreds of masses of this marble that I have exa- 

 mined. I do not, however, assert that such vestiges do not 

 exist in the eastern Pennsylvania marble. 



This very long letter was written principally for the 

 amusement of my learned friend, who, following the foot- 

 steps of the immortal French Pliny, cannot but be interested 

 in hearing any thing that relates to the progress of the great 

 science of natural history. The letter is at your free dis- 

 posal. I am, with very great respect, my dear sir. 



Your friend and humble servant, &c. 

 To M. Lacepede. Bknjamin Smith Barton. 



Philadelphia, October 31, 1802. 



O 2 XXXII. On 



