64 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
stones occur at the top of the bed embedded in the overlying sandstone. 
No glacial striae or facets were seen on any of the exposed pebbles. 
Besides the sandstone pebbles, I saw one of micaceous quartzite, a 
crumpled phyllite, a whitish chert, a red argillaceous sandstone, a 
decomposed granite with reddish feldspar, a silicious schist, im toto 
a variety of rocks indicating the derivation of at least a small portion 
of the débris from the Pre-Devonian terrane. The pebbles could 
hardly have been transported far by water action alone, because the 
sandstones pebbles are of a sort which do not wear well in any stream 
journey. I estimate their journey as stream pebbles to have been 
tens of miles rather than hundreds of miles. ‘The assemblage of these 
pebbles in a well-stratified bed between layers of a coarse-grained 
sandstone leaves no doubt of water action. A few feet of sandstone 
separates this bed from the one above, in which the sandstones peb- 
bles again formed the predominant constituents but were noticeably 
more rounded than the crystalline pebbles. Dr. I. C. White men- 
tions in his Report a bed of boulders at Ponta Grossa and a deposit 
containing fossil wood, but I saw none, nor were such deposits known 
to the Geological Survey staff at the time of my visit. 
Tillite Bed at Conchas: — Conchas lies on the north side of the Rio 
Tibagy about four leagues west from Ponta Grossa. On the south 
_ of the village a small quarry 
7 was opened some years ago 
in a grayish somewhat in- 
durated stony clay bed, a 
boulder-clay phase of the 
tillite beds. The scattered 
pebbles consist of silicious 
rocks and rarely a granitic 
Fic. 15.— Fracture of the tillite bed at Conchas. Pebble. The bed fractures 
with a giant ball structure 
(Fig. 15). No striations were seen on the pebbles. The mode of 
occurrence of the pebbles seems best explained by dropping from 
floating ice and probably the clay with its sand grains of irregular size 
originated in the same manner. The rock when exposed to the weather 
breaks down by a process of checking and the opening of ragged 
fractures into smaller and smaller blocks so that it is valueless for 
building stone. 
This bed overlies the sandstones with waterworn pebbles at Ponta 
Grossa, and recalls in its lithological characters the beds on the south 
of the Rio Jaguaricatu east of Sengéns and also the beds southeast 
of Rio Negro. 
