Q4 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Rio Negro to Lages. The elevations are from aneroid readings and 
are subject to such a correction that the altitude as given may be 100 
feet out. The structure as drawn involves a gentle folding of the trap 
sheets in accordance with the varying dip of the strata between the 
southern edge of the trap and Lages. The inclined bedding seen in 
certain sections exposed in stream bottoms is interpreted as due to 
displacement indicating downthrow along faults or else sharp flexures. 
An interpretation of the structure regarded by the writer as less 
probable than that above given demands the presence of four trap 
sheets and requires the existence of a fault of several hundred feet 
downthrow along the southwestern border of the trap in the upper 
waters of the Rio Canoas. 
In either construction the trap in the pass over the Serra do Espigao 
at the old Collectoria appears as the lowest in the series. The north- 
See ea cg, SANE ey, Fee 
Fic. 26.— Trap ridges of northwestern arm of Serro do Espigaio, seen from 
heights near Corisco. 
western branch of this trappean ridge as seen from the heights near 
Corisco shows three distinct tabular masses rising above a common 
level which may be that of an underlying trap sheet. A four-fold 
division of the trap series is there strongly suggested. The fact that 
one of the great trap sheets may consist of more than one flow without 
intervening beds of sandstone or shale makes it impossible to rely 
implicitly upon topographic profiles. The locality laid too far from 
our route to be geologically examined. 
The lowest bed of trap on this route which I have called the Collec- 
toria sheet is relatively thin, according to a rough estimate given below 
and based on a mule-back transit, about 300 feet. It appears to form 
the surface along the line of the Lages-Rio Negro Road as far south 
as the crossing of the Rio Correntes, where the second sheet or Corisco 
flow is encountered. Along our line of route the upper surface of the 
first flow or sill was not seen and though I am inclined to regard it as 
an effusive sheet I am not able to point out local evidence for such a 
conclusion. 
The Corisco sheet is, according to my rough measurement, the 
thickest of all and has the greatest surface exposure in this district. 
This sheet forms the surface of the plateau along the road from Corisco 
to Coritybanos. The trap is moderately dissected by numerous 
streams. Amygdalar trap abounds on the higher parts of the surface 
