Derby.] 1 * ^ [Feb. 21, 



The Erere group occupies a considerable area in the central plain between 

 tbe mountains of Erere, hut so sub-divided, denuded and disturbed by 

 eruptions of trap, as to present serious difficulties for study, which were, 

 however, overcome by Mr. Smith in 1876, who succeeded in making a com- 

 plete section and in proving, by means of fossils, the unity of the group. 

 Mr. Smith calculated the total thickness at about 200 feet, divided between 

 thirteen distinct beds, of which the greater part consist of fine-grained, 

 micaceous sandstone, disposed in thin beds, with subordinate beds of black 

 shale. The sandstone is generally white or yellowish, but exposed to the 

 weather, it becomes reddish, and the shale often weathers white. Near the 

 base of the group there are a few beds of a compact cherty sandstone, that 

 breaks with great regularity into cubical blocks. Fossils are more or less 

 abundant in all of the beds, those of the shale being different from those of 

 the sandstone. The same beds were met with on the Maecuru and Curua, 

 but less sub-divided, with fewer fossils, and without the shales. The thick- 

 ness of the group on the Curua appears to be less than at Erere. The fauna 

 is very similar to that described from the Maecuru group, but, except in the 

 class of Brachiopods, it is less rich, both in species and individuals. Mr. 

 Rathbun has described twenty-four species of Brachiopods,* two of Trilo- 

 bites, eight of Lamellibranchs and six of Gasteropods.f Of the first some 

 have already been mentioned ; thirteen are limited to this group, of which 

 the most abundant and characteristic are Retzia Jamcsittntt Hartt,:): Reizia 

 Wardiana Hartt, and Discina lodensis Hall. Spirifera Pedroana Hartt, 

 although it appears rarely in the Maecuru group, is, by its abundance, one 

 of the most characteristic fossils of the Erere group. 



The third or Curua group consists almost exclusively of black and red 

 shales, passing at times into shaly sandstone. These beds form low cliffs 

 along the rivers Maecuru and Curua for a considerable distance, lying 

 almost horizontal, except where disturbed by eruptions of diorite. On the 

 Trombetas the black shale forms two short cliffs on the river bank, and the 

 red shale is badly exposed on a lake near by. At Erere these rocks are ex- 

 posed in the eastern part of the plain, and in the base of the serras, par- 

 ticularly that of Tajuri, the front of which is composed almost entirely of 

 these shales. The black shale forms the lowest bed, the thickness of which, 

 on the Curua, is estimated by Mr. Smith at 300 feet. It is well laminated, 

 almost slaty in structure, and in the lower part contains numerous large, cal- 

 careous and arenaceous concretions. The first are bluish black in color, 

 have well developed cone-in-cone structure and emit, when struck with a 

 hammer, a strong odor of petroleum. 



The reddish shale lies above the black, having more or less the same 

 thickness. It is generally chocolate-colored, mottled with spots of a darker 

 hue and banded, parallel with the stratification, with white, yellow or 



* Bulletin of the Buffalo Society of Natural Science, Vol. I, No. 4, 1874. 



i Annals of the Lyceum of Natural History of New York, Vol. XI, May, 1st"). 



.fit. is tint just to mention that the gentleman, to whom this species is dedi- 

 cated, has more than any other, not specially devoted to science, contributed 

 to the progress of geology, not to say of science in general, in Brazil. 



