woodworth: geological expedition to brazil axd chile. 97 



higher sheet. From these observations it is to be inferred that 

 fracturing of the underlying sandstones and the migration of the basic 

 magmas towards the surface went on during the period of great 

 trappean outbreaks presumably with a foundering of a vast area 

 which became flooded with successive sheets of lava from many 

 fissures. Between one and two kilometers south of the dike above 

 described another but much narrower basic dike about a foot wide 

 crosses the mule path near a small stream. An extended search would 

 probably reveal many other dikes once serving as feeders to the over- 

 lying trap sheets. 



The Lages Area. — For several leagues around Lages the trap sheets 

 have been denuded lea\'ing the Triassic sandstones and shales of the 

 Sao Bento beds of Dr. I. C. White's report at the surface apparently 

 in an anticlinal dome. On the northern margin of this tract the trap 

 overlooks it with a well-defined, but much notched, escarpment rising 

 a few hundred feet above the general level. At the eastern limit of 

 vision from the Lages road, a conical outlier of the trap forms a 

 prominent hill, showing that along this line, as on the face of the escarp- 

 ment overlooking the Permian territory, erosion and not faulting has 

 produced the trap escarpment. 



The Lake Basins of Santa Caiharina. — "La province de Santa 

 Catharina est couverte de petits lacs." (Malte-Brun. Geographic 

 1857, 6, p. 687.) In the interstream areas of the trap surface large 

 tracts frequently depart widely in their slopes from the sculptured 

 forms produced by running water. The surface becomes undulating 

 with saucer-shaped pits always opening out on one side towards the 

 drainage way of the district. As the small basins become deeper and 

 more numerous, inosculating rounded ridges rise between them, giv- 

 ing such tracts the appearance of New England kame-kettles and their 

 winding kame-ridges. In the pits there are shallow lakes or pools. 

 These depressions and ridges are evidently the work of long continued 

 secular weathering of the basalt combined with the removal of the 

 products of disintegration and decomposition. 



]\Iost of these basins were at the time of my visit more or less 

 occupied by standing water, some of them forming shallow lakelets 

 in which grew a brilliant green grass. Other basins presented the 

 appearance of level meadows from the filling of presumably residual 

 clay and vegetable matter which they contained. At Sao Joiio on the 

 trap plateau south of Porto da Uniao, a pit some three or four feet 

 in depth had been dug in one of these floored depressions, showing 

 beneath a few inches of vegetable matter a light colored clay evi- 

 dently the product of decomposition of the trap rock. 



