Vol. 50.] OEOLOGY OF MATTO GROSSO. 93 



Limestone is also found in the same range of hills north of Arara, 

 near Diamantino, and still farther north ; see (2), l fcrc Partie, vol. ii. 

 p. 302. 



The limestone occurring between Sao Luiz de Carceres and the 

 Registro do Jauru, (2) 4 &me Partie, pi. 52, may perhaps also belong 

 here. 



In the uppermost Paraguay, near Santa Cruz, Barra dos Bugres, I 

 found some curious pebbles of silicified pisolite and oolite, not im- 

 probably derived from another exposure of the Arara Limestone. 

 The structure is well shown in thin sections. Hartt found pebbles 

 of an apparently similar rock at Aracare, a prominent rocky point 

 iust below Villa Nova in the State of Sergipe, on the Sao Francisco, 

 near its mouth, (9) pp. 396-97. 1 



4. Rizama Sandstone. 2 



This sandstone overlies the Arara Limestone, to which it is appa- 

 rently somewhat unconformable. It is an altered and indurated 

 felspathic rock, very different from the Chapada Sandstones, and 

 is well seen in the line of hills (one of the parallel ridges already 

 referred to) which terminates near the little settlement of Bizama, 

 about 55 kilometres or 34 miles (following the bridle-track) east of 

 Santa Cruz, Barra dos Bugres. This range is divided down the 

 centre b) r a narrow longitudinal valley, which appears to extend 

 for many miles. The same sandstone is found in the adjoining 

 ranges to the east, and also south-west, where one of these parallel 

 ridges abuts on the Rio Paraguay a little above Sao Luiz de Carceres 

 (see Map, PI. VIII.). 



5. Matto Shales. 



These are mainly found west of the uppermost Paraguay, north 

 of its junction with the Rio Sepituba. They appear, however, to 

 occur in the bed of the Rio Jacuara, an eastern tributary of the 

 Paraguay. I could not observe the relations of these shales with 



1 Silicified oolite has also been described from the Assynt Limestone at 

 Stronechrubie, Uamh Valley, Durness ; from Centre County, Pennsylvania, (IS) 

 p. 249 ; and from the neighbourhood of Namur, Belgium, where pebbles of 

 silicified Jurassic limestone occur in Tertiary deposits, (19) p. 404. [I am in- 

 debted to Prof. J. W. Judd, F.B.S., for these references, and the opportunity 

 of seeing hand-specimens and thin sections from the localities mentioned.] 



2 I do not know whether the Bizama Sandstone is represented elsewhere in 

 Brazil. Possibly the compact quartzose sandstone, that unconformably over- 

 lies the limestone ' at Olhos cl' Agua, about seventy-five miles west of Jaeobina,' 

 (9) p. 311, may correspond to it, and not to the Devonian Sandstone of the 

 Chapadas of Matto Grosso and elsewhere. The Bizama Sandstone certainlv 

 appears to occur in the Chiquitos (see infra, p. 96). In stratigraphioal 

 position it may be compared with a great sheet of sandstone in Northern Miuas 

 Geraes and Central Bahia, described by Mr. Orville A. Derby as bent into 

 broad simple folds and lying unconformably on the upturned edges of the 

 Huronian and Laurentian, (13) p. 34, (13) p. 5 ; but he tells me that this sand- 

 stone does not in any way resemble a specimen of the Bizama Sandstone which 

 I sent him. 



