552 SCIENCE PROGRESS 



an ammonium group and another atom is a definite bond 

 located in a fixed position in the compound 



N. .R /R 



N = NT±C< 



N^ \r^ ^R^ 



[xxi] [xxii] 



They claim that there is evidence that this is the case. (Compare 

 Potter and Noyes, /. Anier. Chem. Soc, 191 5, 37, 189.) 



GEOLOGY. By G. W. Tyrrell. F.G.S., A.R.C.S., University, Glasgow. 



Tectonic Geology. — Prof. A. Wegener's hypothesis of lateral 

 drift as an explanation of the present arrangement of the large 

 land masses of the globe still holds the field as a subject of 

 animated controversy. Early land masses are believed by 

 Wegener to have broken along gigantic rifts, of which the 

 Atlantic Ocean is an example ; and the severed portions, 

 floating upon the heavier subjacent stratum of the crust, have 

 drifted farther and farther apart. The former connections 

 are indicated, if not proved, by the amazing correspondences 

 in shape and geological structure between opposite continental 

 masses, as, for example. South America and Africa ; and also 

 by the facts of the present world distribution of plants and 

 animals. The hypothesis does away with the necessity for the 

 huge land bridges across the oceans which have been postulated 

 in order to explain the present distribution of life. 



The greatest success of Wegener's hypothesis has been in 

 explaining the Mesozoic continent of Gondwanaland, with its 

 widespread glaciation, its fresh water and temperate continental 

 sediments, and its typical Glossopteris flora. Hence it has won 

 some acceptance from South African geologists, especially 

 A. du Toit. The fragments of Gondwanaland are now to be 

 recognised in South Africa, Brazil, Falkland Islands, Antarctica, 

 Australia, and Peninsular India. If these remnants have 

 always been where they are at present, the disappearance of 

 the connecting parts is very hard to explain. According to 

 Wegener it would be a physical impossibihty for them to sink 

 into the heavier substrata of the crust. Another great diffi- 

 culty is to explain the glaciation, the traces of which are found 

 in every part of Gondwanaland. Under the hypothesis of an 

 immense southern continent stretching from Brazil to Austraha, 

 and from India to Antarctica, the ice must have spread over 

 enormous areas in equatorial latitudes. If, however, Gond- 

 wanaland was originally only a moderately large continent 



