THE CARBONIFEROUS PERIODS 477 



bowlder clay, often containing smoothed and striated bowlders which 

 in places rest upon a striated and polished pavement of older rocks. 



The glaciated areas were not in the polar regions nor, in many 

 places, at a high altitude, as is shown by the relation of the glacial 

 deposits to strata containing marine fossils. In Australia, for exam- 

 ple, the glacial formations are interbedded with marine sediments. 

 Moreover, coal beds occur in the formation. 



In particular, the Permian glacial deposits occur in the following 

 countries. In India ancient bowlder clay rests, in places, directly 

 upon a striated, roche-moutonnee surface, and some of the glaciated 

 areas extend nearly to sea level. This is remarkable when taken in 

 connection with the fact that the glaciated area is within the tropics. 

 In South Africa the bowlders of the glacial deposit are often striated 

 and rest on a striated rock pavement. In Australia several bowlder 

 beds point to repeated advances of the ice or to several stages of gla- 

 ciation. Thin glacial moraines of Lower Permian age resting upon a 

 glaciated surface of Upper Carboniferous rocks have been discovered 

 in Germany, and Permian bowlder beds in England have been inter- 

 preted as of glacial origin. Bowlder clay of glacial origin occurs in 

 Permian strata in Brazil and Argentina, and conglomerates near Bos- 

 ton, Massachusetts, believed to be in part of glacial origin, are thought 

 to be either of Pennsylvanian or Permian age. 



The exact age of the glacial deposits of India, South Africa, and 

 Australia is somewhat in doubt. They are usually called Permo- 

 Carboniferous and occurred either at the close of the Pennsylvanian 

 or in the Lower Permian. The development of annual rings in Upper 

 Permian trees of certain regions has given rise to the belief in warm 

 summers and cold winters for at least a few thousand years near the 

 close of the period. 



Permian Deserts. — Over large areas of the earth's surface deserts 

 existed in the Lower Permian, as the ripple-marked and sun-cracked 

 red sandstones and shale and the interbedded salt and gypsum tes- 

 tify. Central and western Europe, England, and western North 

 America are known to have been so affected. 



Igneous Activity. — Numerous volcanoes broke out in England dur- 

 ing the period, and the rocks were broken by earthquake shocks, as 

 is shown by earthquake fissures filled with what appears to be Permian 

 sandstone. 



Appalachian Deformation. — In the discussion of the geography 

 of the various periods of the Paleozoic, attention has been called re- 



