CONCLUSIONS AND COMPARISONS 475 



land plain. The various lines of evidence strongly suggest that during 

 the greater part of the year, when not in flood, the surface of the delta 

 was dry and the channels greatly diminished, but doubtless offering 

 sufficient water for the preservation of the amphibian life. With the 

 beginning of seasonal rains the shallow channels would speedily become 

 full to overflowing and the waters spread over large portions of the delta 

 surface in a shallow and braided flood. Following the retreat of the 

 flood waters, an herbiverous vegetation would spring, as by magic, from 

 the loamy soil, only to wither with the advancing dryness. The modern 

 climates suggested by this description are, for one example, the semiarid 

 belts of winter rains, as illustrated in Spain, Italy, and Greece. Another 

 example is given by the monsoon climate of the upper Punjab, a region 

 which receives about half of its annual rainfall during July and August, 

 and during two-thirds of the year, from September to May, is a barren 

 desert. The shrunken rivers then fill but a fraction of their beds and 

 leave the remaining portions as plains of loose sand. This is raised by 

 the strong winds, giving dust storms so thick as to prevent objects a few 

 yards distant from being seen and mantling with eolian sands the dried- 

 out loams and clays of the floodplain. 



The comparison with the upper Punjab may be happily made in regard 

 to the geographic characters also, since here is an alluvial plain stretch- 

 ing away from the Himalayas, approximately 200 miles in width at 

 Delhi, and in the line of the Indus river reaching more than 700 miles 

 through a highly arid region to the Indian ocean. 



The Himalayas,, uplifted after the close of the Eocene and receiving 

 renewed uplifts from time to time, correspond to that vanished generation 

 of the older Appalachians which arose in Upper Devonian times and 

 during that and the following eras wasted away, a portion of its eroded 

 foundations remaining in New England still above the sea. 



The debris of the Himalayas has poured for half of Tertiary and all 

 of Quaternary time into and beyond the great Indo-Gangetic geosyncline. 

 That portion of the waste of the older Appalachians which was shed 

 westward was swept into and sometimes beyond a similarly placed 

 geosyncline, that of the Appalachian basin. The sands and muds of the 

 Devonian alone which were trapped in this axis of subsidence have been 

 computed by Bailey Willis to be equal in volume to the Sierra Nevada.* 



Medlicott and Blanford in 1879 pointed out the fluviatile character 

 of the later Tertiary strata and state that from early Tertiary times the 

 sea has been excluded from the sub-Himalayan region, f where sediments 



• Paleozoic Appalachla. Maryland Geological Survey, vol. 2, 1902, p. 62. 

 t A Manual of the Geology of India, pp. 525-526. 



