chap. xi. Theories on its Origin. 353 



of the Pampean formation having been of estuary 

 origin, can the extraordinary numbers (presently to be 

 alluded to) of the embedded mammiferous remains be 

 explained. 1 



With respect to the first origin of the reddish mud, 

 I will only remark, that the enormous area of Brazil 

 consists in chief part of gneissic and other granitic rocks, 

 which have suffered decomposition, and been converted 

 into a red, gritty, argillaceous mass, to a greater depth 

 than in any other country which I have seen. The 

 mixture of rounded grains, and even of small fragments 

 and pebbles of quartz, in the Pampean mud of Banda 

 Oriental, is evidently due to the neighbouring and 

 underlying primary rocks. The estuary mud was drifted 

 during the Pampean period in a much more southerly 

 source, owing probably to the east and west primary 

 ridges south of the Plata not having been then elevated, 

 than the mud of the Plata at present is ; for it was 

 formerly deposited as far south as the Colorado. The 

 quantity of calcareous matter in this formation, espe- 

 cially in those large districts where the whole mass 

 passes into tosca-rock, is very great : I have already 

 remarked on the close resemblance in external and 

 microscopical appearance between this tosca-rock and 

 the strata at Coquimbo, which have certainly resulted 

 from the decay and attrition of recent shells : 2 I dare 



1 It is almost superfluous to give the numerous cases (for instance, 

 in Sumatra ; Lyell's ' Principles,' vol. iii. p. 325, sixth edit.) of the 

 carcases of animals having been washed out to sea by swollen rivers ; 

 but I may refer to a recent account by Mr. Bettington ('Asiatic Soc.' 

 1845, June 21st), of oxen, deer, and bears being carried into the 

 Gulf of Cambray ; see, also, the account in my ' Journal ' (2nd edit, 

 p. 133) of the numbers of animals drowned in the Plata during the 

 great, often recurrent, droughts. 



2 I may add, that there are nearly similar superficial calcareous 

 beds at King George's Sound in Australia ; and these undoubtedly 

 have been found by the disintegration of marine remains (see Chap- 

 ter VII.). There is, however, something very remarkable in the 

 frequency of superficial, thin beds of earthy calcareous matter, in 



