On the Tertiary Shelh of the Amazons Valley. 59 



form and size were concerned, agreed perfectly with the parasites 

 of Anodonta, but instead of the great number, had only sis 

 suckers on each side. Are these to be regarded as a distinct 

 species? I think not. At any rate, we shall do better to 

 regard this peculiarity as a case of atavism, especially as the 

 two species are not widely distant. In any case the mite with 

 five suckers on each side will have made its appearance earlier 

 in the natiu'al genealogical tree than that with from thirty to 

 forty. But the form with six suckers is a reversion towards 

 the primary form. 



VIII. — The Tertiary Shells of the Amazons Valley. By Henry 

 Woodward, F.G.S., F.Z.S., of the British Museum. 



Of the great river-systems with which explorers have made 

 us acquainted, that of the Amazons is perhaps the most re- 

 markable, as it is also one of the largest in the world. The 

 courses of nearly all the large rivers of om* earth lie in a north 

 and south direction j the Amazons, on the contrary, runs 

 nearly west and east. Situated almost beneath the equator, 

 it traverses the southern continent of America from the eastern 

 slopes of the Andes to the North-Atlantic Ocean (nearly fifty 

 degrees) — a distance, computed by its course, of upwards of 

 4000 miles. Twenty great rivers, all of which are navigable, 

 contribute their waters to its stream, which, under various 

 names, drains considerably more than two millions of square 

 miles of country. It is 40 miles wide where it enters the sea, 

 whilst at 400 miles up stream, to which distance the tide 

 ascends, it is still more than a mile in width*. 



The stratified sandstones and clays observable in this 

 great valley were attributed by Gardner to the Cretaceous 

 series ; Spix and Martins described them as belonging to the 

 Quadersandstein formation f (Upper Cretaceous). By the 

 earlier observers, according to Lyellf, the stratified portions 

 of this series were supposed to be of marine origin, and were 

 successively referred to the Devonian, Triassic, and Tertiary 

 epochs. 



Our own coimtiyman, Henry Walter Bates, who devoted 

 eleven years to the exploration of the natural history of this 

 region, has given us most graphic accounts, in ' the Naturalist 

 on the Amazons,' of the scenery, physical features, &c., but 

 does not dwell much upon its geology. 



It was left to Prof. Agassiz, after his visit to Brazil (1865- 



* Ansted's P%sical Geograpliy, 1867, p. 160, 

 t Hartt, ' Brazil,' p. 484. J Pri 



Principles, vol. i. p. 467. 



