•392 



NATURE 



[July 6, 191 6 



of the plumb-line. What is the meaning of this zone? 

 How has it oome into existence? 



If you look at this section the earth's crust in these 

 outer Himalaya has been compressed laterally : of 

 this there is no doubt. The area between the snowy 

 range and the foothills is a zone of crustal com- 

 pression. And I suggest for your consideration that 

 the Gangetic trough, this zone of deficiency, is a zone 

 of tension in the crust. The crust has been stretched 

 here and attenuated. Here you have compression, and 

 alongside is the tension. The tension is the comple- 

 ment of the compression. I have pointed out that the 

 Himalaya mountains are largely, but not completely, 

 compensated by their underlying deficiencies of 

 density; their compensation is, however, rendered 

 complete by the presence of the Ganges trough ; if 

 the Himalayan compression and the Gangetic tension 

 are considered together, it will be found that there is 

 no extra mass. 



Hypothesis of a Rift. 

 I showed you on the evidence of the plumb-line that 

 the Gangetic trough was a zone of crustal attenuation, 

 a zone in which the earth's crust was deficient in 

 density. I then took one step forward and suggested 

 that it was a zone of tension. I will now take another 

 step forward and suggest to you that there has 

 occurred an actual opening in the subcrust, and that 

 the outer crust has fallen in owing to the failure of its 

 foundations. I suggest that the Ganges plains cover 

 a great rift in the earth's crust. 



The earth is a cooling globe ; an increase of tem- 

 perature occurs as we descend into mines ; and this 

 temperature gradient is a proof that the earth is losing 

 heat by conduction outwards. The discovery of 

 radium has not affected the argument. 



The rock composing the crust and subcrust is, 

 however, a bad conductor, and the interior of the earth 

 will not shrink away from its crust, as has been 

 assumed in the contraction theory. The inner core of 

 the earth is, in fact, not losing heat appreciably. The 

 outer shell was the first to lose its heat, then the 

 shell below it, and the subcrust is now losing its heat 

 more quickly than the interior core. As the outer 

 shells contract from cooling they become too small 

 for the core, and they crack. Supposing we had here 

 a great globe of rock, red-hot throughout ; how would 

 it cool? Can you imagine it cooling in such a way 

 that the core became too small for the outer shell, and 

 the outer shell became wrinkled ? No ; the outer shell 

 would cool first, and would crack. 



The outer shell of the earth was the first to crack 

 millions of years ago ; now a lower shell, the sub- 

 crustal shell, is cracking. When a crack occurs in 

 the subcrust, parts of the upper crust fall in. 



You will see that this. Indus-Ganges trough has the 

 appearance of a crack. And there are reasons for 

 Iselieving that these Himalaya have been split off 

 from this ancient table-land, and have been moved 

 northwards and crumpled up into mountains. 



From the Bay of Bengal to the Mediterranean. 



Geologists have discovered that the ancient table- 

 land of the Vindhyas and Deccan is a remnant of a 

 much greater table-land that in very early ages in- 

 cluded Africa and Arabia. Africa and Arabia and the 

 Deccan table-land are, in fact, fragments of one exten- 

 sive and ancient continent. 



To the west of Karachi we see the Persian Gulf 

 and the plains of the Tigris-Euphrates. The plains 

 of the Tigris-Euphrates are very similar to those of 

 the Ganges: they consist of mud, sand, and. sediment 

 lying in a long trough betv^een the ancient .table-land 

 ■of Arabia and the mountains of Persia. . - 



Further west we find the Euphrates trough is con- 



NO. 2436, VOL. 97] 



tihued by the Mediterranean Sea, and the Mediter- 

 ranean is bounded on the north by the Taurus moun- 

 tains, by the Balkans, Carpathians, Apennines, and 

 Alps. 



Throughout the whole distance from Calcutta to 

 Sicily we see that the old table-land, India-Arabia- 

 Africa, is bounded on the north by a long trough, and 

 that this trough is, in its turn, bounded by the 

 younger mountain ranges from the Himalaya to the 

 Alps. Geologists have discovered that all these moun- 

 tain ranges were elevated in the same era ; they are 

 all of the same age. 



I submit for your consideration that the Ganges- 

 Indus-Euphrates-Mediterranean trough is an indica- 

 tion at the earth's surface of a rift in the subcrust. 



The whole zone from Java to Sicily has been visited 

 by earthquakes throughout the historic period. And 

 the recent earthquakes in Shillong, Dharmsala, and 

 Messina show that seismic activity is continuing in 

 our time. This is, in fact, one of the zones of th© 

 earth along which earthquakes occur most frequently^^ 



The Bombay Coast. ^ 



I must now invite your attention to the Bombay 

 coast. From the Tapti to Cape Comorin runs the 

 range of mountains known as the Western Ghatsl 

 This range is parallel to the coast of India and about 

 40 miles inland ; it rises suddenly with a steep scarp. 

 The strata are almost as horizontal as when first laid 

 down ; they have never been compressed or folded. 



The survey has observed the plumb-line at different 

 points along this coast ; it is always deflected strongly 

 towards the sea. To the west of Bombay and Manga- 

 lore there is the deep sea ; and to the east there is a 

 massive range more than 4000 ft. high ; yet the plumb- 

 line will hang seawards. If the Western Ghats 

 possessed the mass which they appear to possess, and 

 which the Suess school ascribes to them, then the 

 Bombay plumb-line should be deflected 15 seconds 

 towards them. If, on the other hand, the Western 

 Ghats are ooippensated by deficiencies of mass under- 

 lying them in accordance with the compensation 

 theories of Pratt and Hayford, then the plumb-line 

 should hang vertically at Bombay. But the plumb- 

 line takes neither of these courses ; it hangs towards 

 the sea. We have been puzzled for years by the 

 plumb-line at Bombay ; we used to think 

 that the rock under the ocean must be 

 so dense and heavy that it was able to 

 pull the plumb-lines towards the sea. Major 

 Cowie, however, observed in the south of Kathiawar, 

 and found that the plumb-line here had a strong 

 landward deflection. The seaward deflections occur 

 throughout the Bombay coast, but not round Kathia- 

 war. It is only quite recently that we have realised 

 we have at Bombay the same phenomenon as at 

 Lucknow. 



In northern India the plumb-line will persist in 

 hanging away from the visible mountains, and at 

 Bombay it takes the same course, and when I consider 

 its constant seaward deflection I can only suggest to 

 you that a crack in the subcrust has extended from 

 Cape Comorin to Cambay, and that as this crack 

 has occurred the Western Ghats have been elevated. 

 The crack has been filled by masses of fallen rock 

 and bv alluvial deposits brought down by rivers. 



Geologists have shown that this range consists, from 

 latitude 20° to 16°, of the lavas of the Deccan, com- 

 paratively recent rocks, whilst from latitude 16° to 8^ 

 the range consists of ancient metamorphic rocks. The 

 rorks of the northern part of the range are of a 

 different age and structure and origin from 'these of 

 the southern. 



Nevertheless, geodesists contend that this Is one and 



