woodworth: geological expedition to brazil and chile. 67 



a mile east of Lapa the INIorro do Monge (Monk's Hill) rises, the 

 most northern of a series of sandstone ridges forming a line of westward 

 facing escarpment, broken down at intervals by cross-valleys pre- 

 sumably of structural origin. This sandstone overlies the tillite beds, 

 and is traceable in these ridges southward to the Rio Negro, south of 

 which it plunges beneath higher beds, in which, as will be shown, 

 isolated bouklers are not wanting. At the base of the Morro do 

 Monge sandstone, there is a ferruginously spotted variety, which is 

 locally quarried. At the surface it weathers into fist-sized quartzitic 

 knobs. At the top of the tillite series and beneath this sandstone at 

 the northeast angle of the ^Slorro do ISIonge, where the road crosses, 

 there is a conglomerate bed about five feet (1| meters) thick with 

 rounded pebbles in a sandy matrix. This is overlain by one foot of 

 sandstone, then by a bed with scattered pebbles and sandstones. In 

 this series I found a polished quartzose pebble with faint striae. 

 Further south along a private road on the west face of the IMorro and 

 at about the same horizon as the conglomerate beneath the sandstones 

 I found a loose pebble of striated sandstone, a specimen of doubtful 

 indications. Striated pebbles in this locality at this horizon are rare. 



Between Lapa and Rio Negro. — South of Lapa the train runs over 

 the yellow weathered surface of the tillite beds. In a cut between 

 kilometer posts 51 and 52 one or more thin sills of diabase appear. 

 South of the Rio Vargem the train ascends one of the sandstone 

 outliers which is deeply dissected by streams. Between the 73rd and 

 74th kilometer posts on the descent to the valley of the Rio Negro, 

 just under the hard sandstone bed, in a cut a well-defined boulder-bed 

 appears. Some of the rounded masses have a diameter of three feet 

 (1 meter). Occasional cobbles and yellow compact weathered beds 

 at lower levels farther south indicate the continuance of the tillite 

 sands in this direction. 



Localities near Rio Negro: — About two miles north of the city of 

 Rio Negro on the northwest bank of a stream which falls into the Rio 

 Negro there is a high bluff of laminated shales with a pronounced 

 concretionary structure with very small intersecting joints. These 

 shales carry scattered pebbles at various levels, the pebbles ranging 

 up to six inches in diameter. One of these larger pebbles showed a 

 smoothened sole or side and faint striae. These shales lie above the 

 sandstone at the bridge over the Rio Negro at the city of that name.. 

 Some of the pebbles are a hard sandstone; mica schist also occurs. 

 Most of the pebbles were partly rounded, resembling kame and esker 

 pebbles rather than typical stream pebbles. A flattish broken edged 

 piece of sandstone also showed weak striae of glacial character. 



