OF THE SERGIPE-ALAGuAS BASIN OF BUAZIL. 419 



The greater portion of this red mud is derived directlj' from the cliffs along the 

 shores where the ocean is a more direct agent of erosion, transportation and distribu- 

 tion of this material than the streams themselves. I make this statement advisedly. 

 The streams of the region do not now, as a rule, have sufficient current to be such 

 powerful agents of transportation as they formerly were. In the lower portions of 

 their courses they have generally cut down to or near their base levels, and are 

 therefoi-e comparatively powei'less. During the season of I'ains the finer sediments are 

 washed from high grounds into all the streams, but the Rio Sao Francisco is the only 

 stream flowing into the ocean in Brazil south of the Amazon, which brings down any 

 considerable ((uantity of sediment. Such streams as the Scrgipe seldom carry muddy 

 waters into the ocean, the material brought in suspension from the higher country 

 being precipitated near the head of tide water, which is usually miles inland. 



It happens that nearly all these tertiary beds have ahead}' been worn away from 

 the immediate neighborhood of the ocean in the Sergipe-Alagoas basin. They arc 

 well exposed, however, along the coast between Maria Farinha and Parahyba iu 

 cliffs, some of which are more than four hundred feet in height. 



In a few places tertiary beds are exposed along the ocean's beach, having no 

 cousideiable thickness of their own formation overlying them. In such places they 

 offer more than the usual resistance to the encroachment of the sea, and though the 

 beds aie by no means hard, they are worn into fantastic forms by the surf. An ex- 

 ample of this kind is shown in the plate illustrating the erosion of a tertiary beach 

 near Rio Formozo in the province of Pernambuco (y. Plate IV). 



Horizontality of the Beds. — These beds are, everywhere I have seen them, so 

 nearly horizontal that no dip is apparent. Exposures have been seen where the beds 

 appeared, at first sight, to have dips as high as twenty degrees, but upon closer in- 

 spection they have turned out to be delusive. In other places the writer has seen steep 

 dips caused by the caving and tumbling down from l)anks of fragments so large that 

 they might easily deceive the observer into believing them true dips. Pissis gives 

 three examples of dips iu the tertiary, one of which is as high as 15°.''' The cases 

 cited are possibly delusive ones, such as are referred to above, 



Metamorphism in the Ih-tiarrj. — The fiict that there are compact, glassy quartz- 

 itcs among these tertiary beds might, if taken alone, lead one to surmise that this 

 formation had undergone dynamic disturbances. 8uch, however, is not the case. 

 These quartzites seldom or never occur forming beds continuous over considerable 

 distances, but arc derived from soft beds of sandstone which become indurated here 



• .Mcmoirc sur la position g<;,)logiquc, etc., p. 107. 



