102 BULLETIN: MUSEUM OF COMPATATIVE ZOOLOGY. 
placed upon the epoch of dissection. (Branner, 1906, p. 283. A. S. 
Woodward, 1898, p. 63-75). Some warping of the surface has appar- 
ently taken place since the Tertiary beds were deposited. 
At the northern limits of the region under discussion the Serra da 
Mantiqueira rises as a long lofty monadnock range in the Pre-Devonian 
terrane. The western slope of the crest of this gneissic mass subtends 
the surface of contact of the Permian of Sao Paulo upon the same 
ancient rocks. It therefore appears probable that in the Serra da 
Mantiqueira we have a remnant of the Permian floor east of the 
present line of outcrop of those strata. 
Between the Serra do Mar and the escarpment formed by the 
westward dipping Devonian sandstone cuesta! there is a high level 
tract belonging to the planalto or tableland. On the South in the 
headwater region of the Iguassi about Curytiba it is essentially a 
peneplain and swamps of great extent exist locally. But in south- 
eastern Sao Paulo an Atlantic stream, the Rio Ribeira de Iguape, has 
breached the Serra do Mar and gnawed a deep ravine with its head- 
waters pushed against the crystalline Serra da Paranapiacaba for a 
watershed. The situation of this stream, the single example of any 
size to push its headwaters past the Serra do Mar and drain the 
planalto, in the great concave are formed by the Paranapiacaba and the 
Devonian sandstone cuesta is evidently an effect of the Devonian 
sandstone ridge. The almost level crest of this Serra indicates the 
approximate level of the Cretaceous peneplain up to which level the 
plateau was filled with rocks before the present valleys and widened 
out lowlands of the planalto were excavated. Under these conditions 
the Devonian sandstones must have extended much to the eastward, 
possibly to the Serra do Mar crest. In the dissection of the country 
east of the present retreatal escarpment of the Devonian sandstones 
the Rio Ribeira de Iguape, protected from capture by the westward 
flowing streams, has worked backward following the shifting of the 
watershed formed by the retreating cuesta until its headwaters are in 
a position almost to capture the Rio Yapo and the uppermost Iguasst. 
(See map, Fig. 7, p. 48.) The short course and steep gradient of the 
river have enabled it to cut its present profound ravine. A similar 
history probably is true of the Rio Tuberao which in southeastern 
Santa Catharina has excavated its valley across the granitic terrane, 
‘The term cuesta used in a technical sense in North American writings on geo- 
morphology for obvious reasons is not adoptable in Portuguese. ‘‘Costa do outeiro" 
misses the point in the English use of the Spanish name cuesta. Serra monoclina 
expresses in structural terms the essential characteristic of a cuesta. 
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