OF THE SEKCilPE-ALAGUAS BASIN OF BUAZIL. 403 



THE ABi:oLIlOS. 



This locality is described by Prof. Hartt in the American Naturalist, Vol. If, 

 March, 18G8, and in his Geology and Physical Geography of Bi-azil, pp. 174-214. It 

 was not visited by the writer, and the following facts aie taken from Ilartt's writings 

 and from the seiies of photogi-aphs made there in 1876 by j\Ir. Feri-ez, the photog- 

 rapher of the Brazilian Survey. For further details reference should be made to 

 Prof. Hartt's book. 



The sedimentary i-ocks bear a close resemblance lithologically to those of Penedo 

 in the Sergipe-Alagoas basin, and they seem to be referred to the cretaceous largely 

 on account of this resemblance. They are made up of arenaceous limestone (?) be- 

 neath, blue shale above, followed by a yellowish shaly sandstone containing obscure 

 plant impressions. These sedimentary beds are covered by igneous rock, and they 

 all have a north-westerly dip at an angle of from ten to fifteen degrees. Neither 

 the thickness nor the superficial distribution of these rocks is given, but both the size 

 and the height of the islands preclude the possibility of either great thickness or ex- 

 tensive distribution. 



THE BAIIIA BASIN. 



The geology of this basin has been written upon by Pissis, Ilartt, Allj^ort, Derby, 

 Kathbun, Mai-sh, Cope, and White. The description and discussion by Mr. Derby, 

 published in the Archivos do Museu Nacional, Vol. Ill, pp. 135-158, written after 

 the most thorough exploration of the region that has yet been made and with all the 

 facts in hand that had been accumulated by previous observations, is the most nearly 

 complete that has ever been published. 



The cretaceous rocks of the Bahia basin were deposited in a fresh-water lagoon, 

 and are therefore quite distinct from those of the cretaceous beds along other portions 

 of the coast. The limits of the basin have never been determined except in a very 

 general way. The following outlines are taken mainly from Mr. Derby's jiaper above 

 referred to. 



The eastern margin of the basin extends from the city of Bahia to the station of 

 Cat 11 on the Bahia and Siio Francisco railway, a distance of fifty-four miles, '^rhe 

 western limits are buried beneath the tertiary hills near Cachoeira and end somewhere 

 east of Nazareth, while the erosion of these tertiary beds gives the margin of the creta- 

 ceous exposures a ragged edge, outliers or buttcs of the tertiary being scattered here 

 and there throughout the central ])ortion of the area. The northern margin is binied 

 beneath the tirtiary i)lateau which extends from near Cachoeira north of Sto. Amaro, 



