156 Classes of Detritus. 



have visited as in beds or veins, had I adopted my own or> 

 servations as authority. But it has been treated as an ex- 

 tensive stratum by several accurate geologists. See Ameri- 

 can Journal of Science, vol. 7, pp. 31, 32, 44. Marly clay 

 (London clay) is one of the most universal of all visible 

 strata. It is the common clay of all North America. Lieut. 

 A. B. Eaton, of the U. S. army, traced it from the mouth of 

 the Ohio to New Orleans, mostly covered with bagshot 

 sand. No particular localities need be pointed out. It al- 

 ways effervesces with acids when dry. It always contains 

 muriate of lime ; consequently all wells dug in it yield hard 

 waters. Sulphate of magnesia is not uncommon in it ; and 

 in some localities it contains small quantities of muriate of 

 soda. We have one such locality near the Rensselaer 

 school, on the bank of the Hudson. Bagshot sand and 

 Crag are next in extent to the marly clay, and generally 

 overlie it. The sand and crag often pass into each other, 

 and often alternate. If they are ever to be treated as dis- 

 tinct, probably the crag would be considered as uppermost ; 

 for I have never seen the sand uppermost, after ever so ma- 

 ny alternations. The hard-pan of agriculturists is the 

 most perfect crag. Varieties. Brick earth is very perfect 

 in marly clay, on the canal west of Lockport. Hard-pan 

 extends over vast districts of the elevated parts of New 

 England, and New York. Contents. Puddingstone abounds 

 in crag and sand west of Schenectady, and west of Little 

 Falls, along the Erie Canal. Buhrstone is found in the mar- 

 ly clay of Georgia. Bog-ore is found in the bagshot sand 

 from near lake Champlain to Coxackie, along the west line 

 of the Hudson — about eighty miles. Indurated marl is 

 every where in marly clay, in the form of rings and pins. 

 Shell marie is found overlying and imbedded in crag, bag- 

 shot sand, and marly clay ; particularly along the canal be- 

 tween Rome and the Genesee river. 



22. Diluvion. 



No discoveries have yet furnished materials for a subdivi- 

 sion of this general stratum. There is even some difficulty 

 in distinguishing it from post-diluvion. The negative char- 

 acter, that it never contains any works of art, is not a suffi- 

 cient distinction. But, that the pebbles are not separated 

 from the light sediment is a pretty good characteristic. 

 When it is so situated that it could not have been brought 



