S50 A. p. COLEMAN GLACIAL PERIODS AND GEOLOGICAL THEORIES 



past fifty years, and more recently on the fourth also. A very extensive 

 but much scattered literature has grown up regarding it in Indian sur- 

 vey memoirs and records, Australian and South African survey reports 

 and transactions of societies, in the British and German geological jour- 

 nals, and elsewhere; so that it is a serious labor to bring together the 

 published data. Eeferences to most of the literature may be found in 

 articles by Dr David White,* Professor Frech,^ Doctor ISToettling,® And in 

 several of the reports of the Australian Association for the Advancement 

 of Science.^ There is also an important discussion of the subject, mainly 

 from the paleontological point of view, by Doctor Koken, whicn snould 

 be consulted.* 



The widespread development of boulder clay, or "tillite," to use Pro- 

 fessor Penck's convenient term, and in many parts also of underlying 

 striated surfaces, in the three continents first mentioned, are as convinc- 

 ing as those of the Pleistocene ice age in North America and Europe. 



In India the field geologists of the survey have found boulder con- 

 glomerates at many places in the Talchir and Salt range at points 700 

 or 800 miles apart, the two Blandfords and Doctor Oldham being respon- 

 sible for much of the work. In 1885 Doctor Griesbach reported con- 

 glomerates exactl}' like those of the Talchir near Herat, in Afghanistan," 

 extending the limit to a distance of 1,500 miles from the most southeast- 

 erly outcrop in India. Within the Indian empire the ancient boulder 

 clay occurs from latitude 25° to latitude 16° or 17°, and if Griesbach's 

 discovery is included the northward extension reaches latitude 34° or 35°. 



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

 the glacial deposits found near Herat are much like beds found in Eus- 

 sian Turkestan and Elbiirz, in Armenia, suggesting a still farther exten- 

 sion to the west, and that a probably glacial conglomerate is known from 

 the Urals. 



In Australia much attention has been given to the Permo-Carboniferous 

 tillite, which has been traced widely in all the states of the Common- 

 wealth,^" including the island of Tasmania to the south, with a range of 

 latitude between 20° 30' and 43°. Striated rock surfaces are often 

 found under the old boulder cla}'^, the directions of the scorings indicating 



* American Geologist, vol. iii, 1889, pp. 299-330 ; Journal of Geology, vol. xv, 1907, pp. 

 615-633. 



° Lethaea Geognostica, theU I, band ii, pp. 579, etc. 



° Neues Jahrbuch fiir Mineralogie, band ii, 1896, pp. 61-64. 



' Hobart : Vol. ix, 1902, pp. 191-204 ; also vols, vii, viii, and x. 



' Neues Jabrbucb fiir Mineralogie, Festband, 1907, pp. 446, 545. 



' Geological Survey of India, Records, vol. xviii, p. 62. 



10 Australian Association for the Advancement of Science, vol. Ix, 1902, pp. 190, etc. 



