MANSFIELD: ROXBURY CONGLOMERATE. 135 
(1) Smooth and striated rock surfaces or casts of the same. 
(2) Boulders, smooth and striated and faceted by the glacier. 
(3) Morainal material in irregular and unassorted heaps. 
(4) Ice-rafted boulders in the fine sediments of deep water. 
(5) The flora is not conclusive since forests grow close to existing: 
` glaciers and even cover portions of the moraines on their surfaces. 
In the animal remains associated with fine deposits we should expect 
the best records of climatic conditions. 
:— South America. The earlier work of Agassiz and Hartt in 
Brazil led them to believe that there also glacial action had taken place. 
An account is given by Branner of their earlier views and later changes 
of opinion, together with a statement of the facts on which the earlier 
ideas were based, and their true explanation. Large rounded boulders, 
sometimes striated, and supposed to be erratics, were often found 
embedded in what was considered boulder clay. Moreover there was. 
found a widely distributed accumulation of transported, water-worn 
materials, which were believed to be of glacial origin (Branner, p. 759). 
The so-called erratics are shown by Branner to be boulders of decom- 
position, either rounded or subangular, embedded in residual and 
consequently unstratified clays. Soil-creep and landslides tend to 
obscure the true nature of the deposit and the landslides have some- 
times caused well-marked striation and faceting (ibid., p. 761). The 
water-worn materials are shown to be reworked Tertiary deposits 
in which the finer sediments have been washed out and the coarser 
debris left behind by wave action permitted by a Posttertiary depres- 
sion of the land (ibid., p. 768). 
Traces of a Carboniferous glaciation in South America are reported 
by Derby, who notes a resemblance in the characteristics of fossils 
between the Carboniferous formations of southern Brazil and those of 
Australia, India, and South Africa. In the South American rocks 
Derby observed rounded boulders from the size of the fist up to four 
times the size of the head, lying in clay slate and projecting from it: 
In one place he found blocks of various rocks, such as granite and 
gneiss, lying in a stream bed among clay slates. The assemblage of 
such large masses of different materials and the fact that the clay slates 
of the stream banks in the immediate neighborhood contained an 
abundance of smaller blocks convinced him that the boulders had been 
transported. ‘The manner of their occurrence appeared to exclude the 
action of streams or waves, but no striated surfaces had then been 
found on any of the blocks (Derby, p. 175). 
The resemblance of the South American rocks to those of India is. 
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