268 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



Pleistocene. This time of organic stress, curiously, did not affect the polar lauds, but 

 rather those regions bordering the equatorial zone, while the temperate and arctic zones 

 of the northern hemisphere were not glaciated, but seem to have had winters alternating 

 with summers. The lands that were more or less covered with snow and ice lay on each 

 side of the equator — that is, roughly, from 20° to 40° north and south of this line, as may 

 be seen in figure 88. 



Geologists now accept the geographical occurrence of tillite deposits formed in early 

 Permic time as follows: Throughout South Africa (widely distributed and with nuich 

 fossil evidence, thickness of tillites up to 1,130 feet) ; Tasmania; western, southern, eastern, 

 and central Austraha (tillites up to 1,300 feet thick, both land and marine fossils); 

 peninsular and northwestern India; southeastern Brazil (of wide distribution, with land 

 floras and some marine invertebrates ) ; northern Argentina ; and the Falkland Islands. 

 "It may be added that the plant beds of the Gondwana associated with the glacial deposits 

 found near Herat [Afghanistan] are much like beds found in Russian Turkestan and 

 Elburz, in Armenia, suggesting a still farther extension to the west [of India], and that a 

 probably glacial conglomerate is known from the Urals " (Coleman, 1908a: 350). Heritsch 

 records the presence of tillites in the Alps and Freeh points out that a scratched surface 

 occurs in the Ruhr coal field of Germany, on which the Rothhegende rests (Freeh, 1908 : 74) . 

 The Roxbury conglomerate with a thickness of 500 to 600 feet occurs in the vicinity of 

 Boston and is interpreted as a tillite (Sayles and La Forge: 723-4). Then, too, the Lower 

 Permic (Buntsandstein) of western Europe is now thought to indicate not only an arid but 

 probably also a cool chmate. 



The greater part of these glacial deposits is ground moraines or morainic material 

 carried by the land ice into the sea. Their wide distribution in the southern hemisphere 

 clearly indicates that glaciation there was as effective in earliest Permic time as was that 

 of the Pleistocene of the northern hemisphere. This Permic glaciation caused the devel- 

 opment in the southern hemisphere of a pecuhar hardy flora — the Glossopteris flora — of 

 which very little is known in the northern hemisphere. Of this cold-climate flora the 

 invaders and advance niigrants arrived in Asia and Europe not before Middle Permic time. 



In Africa and India the glacial condition appears to have been continuous during early 

 Permic time, and there is as yet no convincing evidence here for interglacial warmer 

 climates such as occurred in the Pleistocene. In Brazil, however, the evidence appears to 

 indicate one warmer between two colder periods, and in New South Wales there is evidence 

 of a series of recurrent colder and warmer climates. This condition is stated by Chamber- 

 lin and Salisbury as follows : 



"In South Australia, above a series of Coal Measures, the plants of which are of the normal 

 Carboniferous types, there is a series of marine beds alternating with beds which contain land 

 plants unlike those of the Coal Measures below. Considerable beds of coal are also included in 

 the series. Interstratified with these marine strata and coal seams there are considerable beds 

 of conglomerate of distinctive glacial type. Some of the bowlders of the conglomerate are striated 

 in such a way as to leave no doubt as to their glacier origin. Furthermore, the substratum on 

 which the bowlder beds rest has been repeatedly observed to be grooved and polished, like roches 

 moutonnees. * * * 



"The number of well-defined bowlder beds is in places (Bacchus Marsh District, Victoria) 

 not less than nine or ten, and some of them have a thickness of fully 200 feet. The marine beds 

 with which they are intercalated have an aggregate thickness of 2,000 feet or more, and 30 to 

 40 feet of coal are included between the highest and lowest of the Ijowldcr beds. The recurrence 

 of the bowlder beds points to the repeated recurrence of glacial conditions, and the great thickness 

 both of clastic beds and of the included coal point to the great duration of the period through which 

 the several glacial epochs were distributed" (632). 



In .Vfrica, in the southern Dwyka region, theie is also some evidence for interglacial 

 warmer periods (Coleman, 1908a: 360). 



