78 The American Geologist. Fobiuary, isi.7 
"leaving- only isolated outliers as a series of table-topped hills 
"or serras, like those of Alraeirira, Parauiquara, Velha Pobre, 
"Aa*. ; that the lake reduced to a lower level, then threw down 
"over the denuded area a sheet of clay, the river finall}' cut- 
"ting its channel through this clay and the underlying sands, 
"etc. He did not claim to have found grooved or striated 
"surfaces on the Amazonas, and the only supposed erratics he 
"discovered were the diorite boulders found on the flank of 
"the Serra of Erere." 
To this Hartt could not give his assent and in the same 
paper he said: "To speak broadly, I did not see either at 
"Erere or in any part of the Amazonas anj'thing that would 
"suggest glacial action. So far as the province of Para is 
"concerned, the clays, sands, etc., forming the lower lands are 
"far from being uniformly distributed and are very puzzling 
"to study. The arrangement of the materials varies in differ- 
"ent regions, and many of the deposits are local. In part the 
"lower lands are formed from the material derived from the 
"wearing down of the great sheet of clays, etc., of which the 
"Almeyrim and Santarem hills are relics; in part they are of 
"brackish or fresh water origin deposited when the river stood 
"at a greater hight; and much is the very recent work of the 
"river. The variegated cla3's are not all of the same age. 
"Superficially examined they appear to be universally distrib- 
"uted, but it is very far from being the case. It is impossible 
"to recognize and trace beds of clay in the Amazonian valley 
"with the aid of lithological characteristics alone. It is suffi- 
"cient to say that variegated clays of exactl}'^ the same ap- 
"pearance and structure, because formed of materials which 
"have been reworked or were originally drawn from the same 
"source, occur in the Devonian, Carboniferous, Tertiary, and 
"in half a dozen successive formations of recent times. 
"I have referred the beds of the table-topped hills to the 
"Tertiary. Some of the clays and sandstones of the lower 
"Amazonas may also be later Tertiary; but many are un- 
"doubtedly recent, as they are full of leaves of modern species. 
"Near Santarem I found a bed of fresh water mussels, Casta- 
^'lea, Hyarea, Unio, etc.. whose upper limit was at least fifty 
"feet above the level of the highest Amazonian floods. This 
"is in exact accord with the facts I have given elsewhere bear- 
