94 bulletin: mtjseltim of comparative zoology. 



Rio Negro to Lages. The eleA-ations 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 

 Avaters 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- 



FiG. 26. — Trap ridges of northwestern arm of Serro do Espigao, 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, Avhere the second sheet or Corisco 

 flow is encountered. Along our line of route the upper surface of the 

 first floAv 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 



