208 Annals of the Carnegie Museum. 



that shown on Plate IX, fig. 2, which form convenient storage tanks 

 for water. These can not be considered as potholes produced by 

 stream action, because they are not suggestively situated with respect 

 to drainage channels. The holes are considered by Dr. Branner to 

 have been produced by the action of organic acids in disintegrating 

 the less resistant spots in the rock, and the removal of the material 

 by the overflow of muddy waters in the same way that the basins on 

 granite hills near Quixada in Ceara may be explained. Some of 

 these basins have also been cleaned out by man to serve as storage 

 reservoirs for water.-^ 



The Jacobina range is of quart^ite and schist, flanked by gneiss and 

 granite. So far as is known to the writer the relation of the quartzite 

 and other altered sedimentary rocks which have been named the Minas 

 Series, to the Ceara series of similar materials, farther north, has not 

 been determined. The structure of the range has been discussed by 

 Dr. Branner,'-^ who regards it as being composed of blocks of quartzite. 

 Subsidiary ledges of quartzite wherever observed have strike conform- 

 able with that of the main range. To the northwest there are promi- 

 nent though minor cjuartzite ridges between Itumirim and Angico. 

 To the east such ridges were noted by the writer at Palmerinhas, and 

 at Morro da Maravilha. Approximately as far east of Serra da Itiuba 

 as Serra de Jacobina is west of that range, there is a range of hills 

 culminating at the south in a hill at Monte Santo which rises three 

 hundred meters above the plain. This hill has a core of quartzite, 

 standing nearly vertical, with strike N. io° E., magnetic, or about 

 N. 5° \V., true. 



A range of serras farther east, extending from south of Cumbe 

 nearly to Canudos, and composed in part of quartzite, have been 

 described by Soper.^^ Earlier discussions of the structure of Serra 

 Itabaiana have been published by Dr. Branner.^" 



West of the Bay of Bahia, along the railway which runs north from 

 Cachoeira to Feira de Sant' Anna, gneiss and granite are exposed, but 



-' Geologia Elementar por J. C. Branner, 2d ed., pp. 50-51. Rio, 1915. 



-* The Geology and Topography of the Serra de Jacobina, State of Bahia, Brazil, 

 by John C. Branner, Am. Jour. Set., Dec, 1910, pp. 385-392. 



2^ Publ. No. 34 of the Inspectoria, pp. 19-25. 



^o The Cretaceous and Tertiary Geology of the Sergipe-Alagoas basin of Brazil, 

 Trans. Am. Phil. Soc, Vol. XVI, 1889, pp.. 379-382. 



The Geography of Northeastern Bahia, Brazil, The Geographical Journal. Aiig.- 

 Sept., 1911, pp. 145-148. 



