Derby.] *-tv |Feb. 21, 



scoriaceous appearance, and enclosing crystals of quartz and fragments of 

 the adjacent sedimentary rocks, these last being often so slightly metamor 

 phosed, as to still preserve traces of fossils. The beds traversed by the 

 dykes are somewhat altered, for a distance of a few feet from the point of 

 contact. 



The Tertiary beds have been so often mentioned in the course of this ar- 

 ticle, that little remains to be said regarding their character and distribution. 

 They are distinguished from those of the older formations by their hori- 

 zontal position, and by the absence of fossils and of eruptive rocks. They 

 consist of sandstones and clays, of brilliant and varied colors, SUCb as 

 white, red, yellow and blue, combined in different shades, so as to produce 

 a very striking effect in the clid's, which are very frequent along the tribu- 

 taries, but rare along the main river. The rock is in general very slightly 

 consolidated, except an occasional bed or patch, in which a cement of 

 ■ >xide of iron has produced the coarse ferruginous sandstone, found scatter- 

 ed over the surface thoughout the whole of the Amazonian highlands. 



The Tertiary series is best presented in the serras known under the col- 

 lective name of Serras de Parti, which are seen from the river, from Ahnei- 

 rim to near Prainha. These are mountains of circumdenudation, perfectly 

 level on top, and of an elevation of about 1,000 feet. The one nearest to 

 Prainha, called Parauaquara, was visited by Prof Hartt in 1871, who 

 found the structure well presented in the steep, bare front of the mountain. 

 The beds, whose thickness corresponds approximately to the height of the 

 mountain, consist of sandstones and clays, of various colors, disposed in 

 nine distinct divisions. From Parauaquara westward, the series of table- 

 topped hills extend for a long distance, but, lying farther back from the 

 river, they cannot he seen, except from some high point as, for example, 

 the mountains of Erere. From the Maecuru, I saw a rounded peak, rising 

 above the general level, apparently an island of some older formation, in a 

 sea of Tertiary sandstone. In the vicinity of Monte Alegre there are de- 

 posits identical in character with those of Parauaquara, which were evidently 

 laid down after the elevation of the Erere anticlinal. These deposits, like 

 those of Alenguer and Obydos, have suffered a destructive denudation, 

 which has considerably reduced their original height, which probably was 

 never equal to that of the Serras of Paru. 



The Tertiary beds of the southern side of the valley, are, in the Santarem 

 region, considerably lower than those of the north, the difference being 

 probably due to the inclination of the bottom of the Tertian" sea, and the 

 smaller quantity of sediment received by the regions farthest removed 

 from the margin of that sea, The highlands behind Santarem are 400 

 feet high, and do not appear to have suffered denudation that has dimin- 

 ished sensibly their original height. In a bed of blue chry, exposed on the 

 slope of these highlands, I found worm tubes, the only fossils that the 

 Tertiary beds of this region have yet afforded. 



This lack of fossils is noticeable, not only in the Lower Amazonian region, 

 but throughout Brazil. In every province there are beds similar in charac- 



