Page:The Journal of geology (IA journalofgeology11893univers).pdf/345
These materials are made up of boulders, cobbles, and gravels, sometimes assorted and sometimes having sand and clay mixed with them, and are spread far and wide, though irregularly, over all the Tertiary and Cretaceous area bordering the ocean, and extend for a long distance into the interior, and far beyond the borders of the Tertiary deposits. They were regarded by the writers in question as analogous to the water-worn materials so common in the northern drift. Had these materials been of glacial origin it is not unreasonable to expect that striated pebbles would have been found among them occasionally, but, as a matter of fact, no such marks have ever been found, though I have made the most diligent search for them. That the striæ have been oblitered by weathering agencies is out of the question, because the preservation of the water-worn and pitted faces of the pebbles shows plainly enough that striated faces would have been preserved equally well had they ever existed. The origin of these water-worn materials has already been explained elsewhere, and from that article the following quotation is made:[1]
"This formation is spread over the hills and valleys of the Sergipe-Alagôas basin and over the adjacent country in the form of a thin coating of cobblestones, pebbles and sand, sometimes loose and sometimes cemented into a pudding-stone as much as ten feet in thickness, and, when exposed, stained black by manganese. It caps the summit of the tertiary plateaux or their outliers, and it is frequently strewn along down the sides of hills and accumulated in the valleys. It is not confined to the geographic limits of the Cretaceous or Tertiary, but is found further inland and far beyond the present limits of these formations. It is everywhere more or less irregular in thickness, and nowhere can it be said to be universal or continuous. The writer has seen this material throughout Sergipe and Alagôas, in Parahyba, and as far inland as the head waters of the Rio Ipanema in the interior of the province of Pernambuco, where there is no remnant of stratified Tertiary beds. Between the lower Rio São Francisco and the frontier of the province of Alagôas, and indeed in many parts of the province of Pernambuco, this water-worn material is found mingled in bogs with the remains of extinct, gigantic mammals.
One of the marked characteristics of this post-tertiary formation is that it is much coarser inland, and grows finer as the coast is approached. The- ↑ Trans. Amer. Phil. Soc., 1889, XVI., 421.