60 bulletin: artseitai of comparative zoology. 



eastern limits of the Capivary sandstone group. If this interpretation 

 of the structure be correct and the shale bed does not dip into the sec- 

 tion immediately westward of this exposure, the question is raised 

 whether it is not a southeastern outlier of the shales which certainly 

 overlie the group westward from Rio das Pedras. In this case the 

 sandstone beds northwestward from Elias Fausto to this shale outcrop 

 instead of being 1,400 feet thick would have a thickness not greater 

 than that of the second belt above the base, i. c. about 600 feet. 

 This would reduce the total thickness of the section measured from 

 4,000 ft. to 3,200 feet. 



As for the maximum thickness, neglecting the above possible causes 

 of diminution in the estimated thickness, there is the presumption that 

 the sill of diabase which crops out between the 230 and 231 kilometer 

 posts in the form of a bright red terra roxa zone represents the trap 

 sheet which forms the falls in the river at Piracicaba. The upper 

 contact of this layer on the southeast is near the 575 M. contour; on 

 the northwest down the dip at the river it is somewhere near 525 M., 

 giving a drop of 50 M. in 7.5 kilometers or thirty-five ieet to the mile, 

 which is equivalent to a little more than a dip of 1° to the northwest, 

 and since the strata overlying the sill are presumably parallel to the 

 plane of the sill, we have in this part of the section an estimate of the 

 dip. Again the thin bed of shales at and southeast of Elias Fausto 

 Station have a breadth of outcrop of four kilometers (2.48 miles, say 

 2.5 miles). Their base on the east along the line of the railway is at 

 about the 600 M. line; their top at the northwest at 575 M. giving 

 a fall of the surface of twenty-five M. in four kilometers or eighty-two 

 feet in 2.5 miles, or thirty-two feet to the mile. Assuming the shale 

 bed to be at least ten feet thick, we should have dip of thirty-six feet 

 to the mile, which considering the approximations on which the esti- 

 mate is based is in close accordance with the estimate of the dip made 

 for the beds immediately southeast from Piracicaba. 



On the assumption of continuity of bedding and dip from the base at 

 Itaicy to Piracicaba, a dip of 1° would give a minimum thickness of 

 1,145 M. or 3,700 feet for the total thickness from the base to the 

 Stereosternum beds. 



Rough calculations of the mainly sandstone group at the base about 

 Imbaiatuba with a breadth of outcrop of 5.76 M. or 4.19 miles gives an 

 estimate of 436 feet for their thickness, with a maximum of 700 when 

 scaled to the maximum estimate. 



The succeeding shale bed 153 feet as a minimun, 226 as a maximum. 



The second group of sandstones may be estimated as having at the 

 minimum a thickness of 400 feet, a maximum of 600 feet. 



