



*, 











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1ft' 



% 



atie 



A life 



mist 







ne 

 din 



mains 



itions 



.'their I 



.nother. 

 f a tur- 



Janet 



■rder . 



jnrto 



lied tie 

 at I" 



am 

 ft 



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the 



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13' 



Ch. XIX.] 



ITS I'OEMATIOXS. 



467 



Amazons 



The lowest is a sandstone, the next above a series of finely 

 laminated clays of various colours, and containing well-pre- 

 served leaves of plants supposed to belong to the existing 

 vegetation of the country. These clays pass upwards into 

 sands and sandstone, occasionally divided by an argillaceous 

 layer, and at some points, as at Obydos, calcareous beds occur 

 with freshwater bivalve shells of existing species. Over this 

 occurs the third deposit, which appears to me, from the des- 

 cription given of it by Agassiz, to resemble in __ 

 inundation -mud or loess, and in others the produce of land- 

 floods, which, after denuding the subjacent sandstone, have 

 left masses of unstratified materials to level up the uneven sur- 

 face of the denuded strata. The above-mentioned formations 

 have been traced, according to Agassiz, over an area 3,000 

 miles in length and 700 in breadth, and their united thick- 

 ness exceeds 800 feet. By the earlier observers the stratified 



some 



marine 



and were successively referred to the Devonian, Triassic, and 

 Tertiary epochs ; but Agassiz ascertained that they were of 



Tn Arl A tit-* rlnf a *~% -*s-\ ^ «■>*-• 1~ ^ ^ _ ^ "1 _ ^ 1 T i • . • 



examm 



ing them, of freshwater origin. The Obydos fossils above 

 alluded to, which former travellers ascribed to the genera 

 Avicula, Solen, and Area, are in reality, according to Agassiz, 



of species now living in the Amazons. Mr 



Naiades^ o 

 mentioned 



Martius 



of the same formation, which occur nearer the sea and are used 

 for making lime, to be of marine origin. These shell-beds are 

 found at the mouth of the Tocantins, on the island of Marajo 

 and towards the sea coast near Vigia. From the latter place 

 Mr. Bates himself procured lar^e marine univalve of «™t.i™ 



them 



These several state- 



ments appear to me to be perfectly consistent with each 

 other and with that passage from freshwater to marine de- 

 posits which we find in the alluvial plains and deltas of great 



- 



jitfdti;ts a 66 HiBU>ry on ' :vlloj of a °"« m ' Aa »' ic *>»«* «»• «* 



H U 2 



