A MA ZONIA N UPPER CA RB ONIFER O US FA UNA . 



highlands from either side to, or near, the banks of the great 

 river. The supposed Archean, which appears in the rapid sec- 

 tion of the Tapajos on the south and of the Trombetas on the 

 north, consists on the former river of metamorphosed quartzites 

 and porphyritic eruptives, and on the latter of syenite and simi- 

 lar porphyritic eruptives. The latter prove on microscopic 

 examination to be much altered plagioclase rocks, presumably 



y.'.'.'.'A Arrhenu ,' ' J 



Upper Silurian H 



i^M^i Cretaceous 



I Devonian lliilll 

 23 Terfiai y 



Cow honiferous 



augite-porphyrites. Resting on these are, on the Trombetas, 

 slightly disturbed sandstone beds with Upper Silurian fossils. 

 Below them comes a zone of sandstone and shales with Spiro- 

 phyton, which has been better explored on the Curua and Maecuru 

 and at the foot of the small Serra de Erere near Monte Alegre, 

 where an abundant Devonian fauna has been found. Beds with 

 Spirophyton have also been observed on the Tapajos below the 

 falls, and these, originally supposed to be Carboniferous, are now 

 referred to the Devonian. The best explored Carboniferous 

 locality is on the Tapajos at the village of Itaituba and the neigh- 

 boring limestone cavern of Bom Jardim, where five fossil-bear- 



