272 ANNUAL OF SCIENTIFIC DISCOVERY. 



It is true that over by far the larger part of the globe these agi- 

 tations are either slight or else absolutely imperceptible, so that 

 we consider the greater portion of the earth as motionless; but 

 there are other countries that have again and again been rudely 

 shaken by violent and destructive convulsions. These are the 

 true regions of the earthquake and volcano, and modern physical 

 geography has made such progress as to mark off a certain num- 

 ber of extensive districts or zones in which the shocks are simulta- 

 neous. Among these may be mentioned the Atlantic district, that 

 of Central Asia and that of the Pacific Ocean. 



SUMMARY OF GEOLOGICAL FACTS. 



Niagara Falls. — Some geologists predict a great change in the 

 character of these falls. The hard limestone over which the wa- 

 ter passes is slowly wearing away, and the current in some places 

 about 800 yards above the Canadian fall has obtained access to 

 the soft shales underneath, which are rapidly eaten away. It has 

 been surmised that a subterranean stream of water is now pouring 

 into the gulf below the falls, and that the " Horseshoe" shelf will 

 ere long be undermined and destroyed. When this occurs the 

 falls will be converted into a rapid, and the great mass of water 

 will be diverted from the American to the Canadian shore. 



Cretaceous Sea in Italy. — Prof. Seguenza has shown that the 

 middle cretaceous deposits of Central Italy correspond completely 

 with the cretaceous rocks of Algeria, of the zone of Ammonites 

 Rothomageihsis. As showing the similarity of geological conditions, 

 he says that of 44 species of Italian fossils, 43 occur also in the 

 African formation. He seems justified, therefore, in the conclu- 

 sion that the middle cretaceous sea extended from Central Italy to 

 the Province of Constantine. 



Oold-Jields of South Africa. — Gold has been extensively dis- 

 covered in Africa, between 17° and 21.30° S., and about 400 miles 

 from Pretoria, the nearest point of civilization in the S. African 

 Republic of Transvaal. The Kingdom of Sofala, on the coast, to 

 the eastward of the alleged gold formation, has been considered 

 as the Ophir of Solomon's time. It is stated that the gold is found 

 in quartz veins, and that the fields are of vast extent. The natives 

 from old times have brought gold to the Portuguese in quills ; they 

 are said to light large fires to loosen the rock containing visible 

 gold, and then further disintegrate it with their " machetes." 



Thickness of the Earth''s Crust. — Herr Sartorius von Walters- 

 hausen, of Gottingen, from recent calculations, stated before the 

 British Association, in 1868, that he inclined to the belief that the 

 thickness of the earth's crust was 14 geographical miles. He 

 also expressed the conviction that, at the time of the first forma- 

 tion of the seas, the thickness did not exceed 50 metres. 



Discovery of a Mastodon. — A short time ago Captain Boutelle, 

 of the United States Coast Surve}', discovered on the beach of St. 

 Helena Island, near low-water mark, and not far from where the 

 City of Port Ro^'al has been laid out, the remains of a mastodon 



