ation of the actual phenomena, I trust that,
in presenting for the first time the formations of the Amazonian basin
in their natural connection and sequence, as consisting of three uniform
sets of comparatively recent deposits, extending throughout the whole
valley, the investigations here recorded have contributed something to
the results of modern geology.

FOOTNOTES:

[A] Bohn's edition of Humboldt's Personal Narrative, p. 134. Humboldt
alludes to these formations repeatedly; it is true that he refers them
to the ancient conglomerates of the Devonian age, but his description
agrees so perfectly with what I have observed along the banks of the
Amazons, that there can be no doubt he speaks of the same thing. He
wrote at a time when many of the results of modern geology were unknown,
and his explanation of the phenomena was then perfectly natural. The
passage from which the few lines in the text are taken shows that these
deposits extend even to the Llanos.

[B] I am aware that Bates mentions having heard, that at Obydos
calcareous layers, thickly studded with marine shells, had been found
interstratified with the clay, but he did not himself examine the
strata. The Obydos shells are not marine, but are fresh-water Unios,
greatly resembling Aviculas, Solens, and Arcas. Such would-be marine
fossils have been brought to me from the shore opposite to Obydos, near
Santarem, and I have readily recognised them for what they truly are,
fresh-water shells of the family of Naiades. I have myself collected
specimens of these shells in the clay beds along the banks of the
Solimoens, near Teffe, and might have mistaken them for fossils of that
formation had I not known how Naiades burrow in the mud. Their
resemblance to the marine genera mentioned above is very remarkable, and
the mistake as to their true zoological character is as natural as that
by which earlier ichthyologists, and even travellers of very recent
date, have confounded some fresh-water fishes from the Upper Amazons of
the genus Pterophyllum (Heckel) with the marine genus Platax.

[C] As I have stated in the beginning, I am satisfied that the
unstratified clay deposit of Rio and its vicinity is genuine glacial
drift, resulting from the grinding of the loose materials interposed
between the glacier and the solid rock in place, and retaining to this
day the position in which it was left by the ice. Like all such
accumulations, it is totally free from stratificatio