PEISICAL OEOORAPHY OF ABYSSINIA. 157 



Of the lakes of Abyssinia, only one was reached by 

 the expedition; and this, Lake Ashangi, unfortunately 



been made — with that of any well-known tract in the tropics, such as British 

 India. I select this for comparison, because I am best acquainted with the 

 facts, and do not need to take them at second-hand. In the British islands 

 the average rainfall is about twenty-four inches distributed over the greater 

 portion of the year. In India it averages over the whole country about fifty 

 inches, by far the greater portion of which falls in three months. The showers 

 are far heavier, and far more effective in sweeping soO, sand, and pebbles from 

 the surface of the country into the streams ; and floods in the latter are of 

 annual occurrence, instead of only happening at rare intervals. The effect of 

 a river in full flood in sweeping detritus down into the sea compared with the 

 usual denudating action, is as the comparison of the effect produced by the 

 breakers of the ocean in a storm to those of an inland sea on an ordinarily 

 fair day. In flood, a river is liquid mud rather than water. But, in addition 

 to the great floods, minor floods in tropical streams are matters frequently of 

 daily occurrence during the rainy season. That precisely the same pheno- 

 mena occur in Abyssinia as in India I had ailiple opportunities of seeing in 

 July and August ; indeed, they are notoriously the rule in all tropical 

 countries, except the few rainless regions. 



But this is only one element in the comparison. It must be borne ia mind 

 that fresh- water denudation is distinctly antagonistic to marine ; and where 

 the former is large, the quantity of detritus carried down to the sea by 

 rivers actually protects the rocks of the coast from destruction. The coasts of 

 Abyssinia are so little exposed and so much defended by coral islands that they 

 could not under any circumstances afford a fair opportunity for judging, even 

 if the drainage of the country were not in the other direction. The coasts of 

 the peninsula of Hindustan, however, are an excellent case in point. Along 

 the whole eastern side of the peninsula, from the head of the Bay of Bengal 

 to far south of Tanjore, at all events, the whole coast is fringed by alluvial 

 deposits, except in one spot, close to Vizagapatam, where alone the sea washes 

 away rock. Nearly all the great rivers of the peninsula pour their detritus 

 into the sea on the east coast ; but even on the west coast, where fewer and 

 smaller streams, for the most part, enter the sea, there is throughout a very 

 large extent of shore a similar alluvial belt. Further north, in Guzerat, 

 Kattiawar, Cutch, and Sinde, the coast is in most places formed of alluvial 

 •deposits derived from the large rivers Indus, Nerbudda, Taptee, Mhyr, &c. ; 

 and throughout the whole immense shore line of British India, exclusive of 

 the Burmese provinces, the only places where any marine denudation takes 

 place are between Bulsar, south of Surat, and Mangalore, and at a few 

 isolated points further south oh the west coast, and at Vizagapatam on the 



