woodworth: geological expedition to brazil and chile. 79 



of true boulder-clays is the earthy type of tilllte seen in the vicinity of 

 Rio Negro. This I belie\e was deposited by floating ice in a shallow 

 sea Avithout stratification. 



There are nian^- beds composed of small rock particles embedded in 

 an argillaceous ground-mass carrying only occasional striated stones 

 which present some of the characters of flood deposits but which by 

 reason of their glacial features it is to be presumed are tillite. In 

 their yellow weathered state, their diagnosis is made with difficulty. 

 They grade into "mealy" yellow sandstones. 



The group of stratified gravels appears to be represented in the 

 Orleans basin by the small ridge of conglomerate whose cross-section 

 and horizontal extension recalls the form of an esker. The other 

 occurrences of conglomerates as at Ponta Grossa do not show topo- 

 graphic features which enables one to distinguish them from gravels 

 of non-glacial origin. 



The dark colored shales in the Permian series, on the whole much 

 less developed in thickness than the coarse sediments, have not been 

 studied with reference to their glacial derivation. Where they con- 

 tain marine fossils it is to be presumed that they have been worked 

 over and any original glacial characteristic has been dost. Some of 

 the fine clayey lieds of sandy aspect which behave like loess in their 

 weathered condition I suspect were originally loess, but this determina- 

 tion is difficult to make. 



The large content of clay in the tillite beds of Jaguaricatu and 

 Conchas on the Tibagy is not consonant with the derivation of these 

 beds from the granites and gneisses of the present Serra do Mar 

 region since such rocks under the direct attack of glaciation would 

 produce predominantly gravelly and sandy beds with a minimum of 

 clay or rock-flour of an argillaceous character. For this reason I am 

 disposed to regard these clayey tills as worked over from the under- 

 lying Devonian shales and from the slates of the Pre-Cambrian series. 

 This makes it possible to suppose that much of the material did not 

 come from any great distance to the east of the Serra do Mar. 



The tillite beds which approach nearest in their lithological charac- 

 ters to a solidified boulder-claj^ appear when fresh of a bluish color 

 somewhat darker than the hue of the glacial brick clays of many parts 

 of the United States of America. On exposure the rock weathers to a 

 light brown or yellowish brown color often with streaks of reddish 

 iron oxide. 



This rock joints irregularly; frequently its fracture assumes a 

 curving plate-like structure tending toward the dome structure and 



