100 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
or of the locally baselevelled tracts developed betweer 
the more resistent members of the tableland. The an- 
nexed diagram of the mountain crests as seen rising 
above the lowland east of Curityba is typical of the 
region for many leagues northward into the state of Sao 
Paulo. 
Isolated summits in this region rise somewhat above the 
level of the trap plateau. It is probable that in the late 
Mesozoic baselevelling of the region the granitic bosses 
and some of the gneissic areas were not reduced to the 
general level. On thenorth the lofty Serra da Mantiqueira 
culminating in Mt. Itatiaia nearly 10,000 feet in eleva- 
tion, warrants this statement. 
The slope from the crest of the Serra do Mar to the sea 
is generally steep. It is deeply ravined by short streams. 
The interstream areas form sharp spurs which in some 
portions of the slope are deeply dissected, standing out as 
isolated peaks and mountain blocks as on the south side 
of the harbor of Rio de Janeiro. The immediate descent 
to the sea is often so precipitous and the relief so high 
that where the geological structure is permissive of the 
hypothesis down-faulting on the ocean side has been advo- . 
cated as by Dr. Derby as a factor in the production of 
the topography. 
This deeply dissected slope has been depressed beneath 
sea-level since its dissection arrived at an advanced stage. 
The submerged valleys form harbors and reentrants such 
as those of Rio de Janeiro,Santos, Itajahy, Sao Francisco, 
and Florianopolis.!. Since this depression in relation to 
sea-level took place, a slight uplift of about ten feet (3 
meters) has occurred, raising up in the form of a plat- 
form about bay shores a recent deposit of littoral sands, 
D 
ZL 
LLL 
1 The frequent repetition of the circumlocutions one is obliged to 
employ in expressing concisely the fact of our ignorance as to whether 
the land has sunk or the sea-surface risen when reference is made to a 
change of level of land and sea becomes intolerable in writing at length 
of such matters. Suess’s terminology partially avoids the embarrass- 
ment but does not provide a name for a change of level of land and sea. 
The French term denivellement, a variation of level, suggests the use in 
English of its natural equivalent delevelling in analogy with baselevelling. 
A positive delevelling thus becomes a depression of the land in relation 
to the sea-level, and a negative delevelling an apparent elevation of the 
land in relation to the surface of the sea. 
Fic. 28.— Crests of the Serra do Mar seen from the west on the tableland near Curityba, Parané. 
