; 
a 
: 
WOODWORTH: GEOLOGICAL EXPEDITION TO BRAZIL AND CHILE. 79 
of true boulder-clays is the earthy type of tillite seen in the vicinity of 
Rio Negro. This I believe was deposited by floating ice in a shallow 
sea without stratification. 
There are many beds composed of small rock particles embedded in 
an argillaceous ground-mass carrying only occasional striated stones 
which present some of the characters of flood deposits but which by 
reason of their glacial features it is to be presumed are tillite. In 
their yellow weathered state, their diagnosis is made with difficulty. 
They grade into “mealy”’ yellow sandstones. 
The group of stratified gravels appears to be represented in the 
Orleans basin by the small ridge of conglomerate whose cross-section 
and horizontal extension recalls the form of an esker. The other 
occurrences of conglomerates as at Ponta Grossa do not show topo- 
graphic features which enables one to distinguish them from gravels 
of non-glacial origin. 
The dark colored shales in the Permian series, on the whole much 
less developed in thickness than the coarse sediments, have not been 
studied with reference to their glacial derivation. Where they con- 
tain marine fossils it is to be presumed that they have been worked 
over and any original glacial characteristic has been lost. Some of 
the fine clayey beds of sandy aspect which behave like loess in their 
weathered condition I suspect were originally loess, but this determina- 
tion is difficult to make. 
The large content of clay in the tillite beds of Jaguaricatu and 
Conchas on the Tibagy is not consonant with the derivation of these 
beds from the granites and gneisses of the present Serra do Mar 
region since such rocks under the direct attack of glaciation would 
produce predominantly gravelly and sandy beds with a minimum of 
clay or rock-flour of an argillaceous character. For this reason I am 
disposed to regard these clayey tills as worked over from the under- 
lying Devonian shales and from the slates of the Pre-Cambrian series. 
This makes it possible to suppose that much of the material did not 
come from any great distance to the east of the Serra do Mar. 
The tillite beds which approach nearest in their lithological charac- 
ters to a solidified boulder-clay appear when fresh of a bluish color 
somewhat darker than the hue of the glacial brick clays of many parts. 
of the United States of America. On exposure the rock weathers to a 
light brown or yellowish brown color often with streaks of reddish 
iron oxide. 
This rock joints irregularly; frequently its fracture assumes a 
curving plate-like structure tending toward the dome structure and 
