34 A. BLYTT. [NO. 1. 



beacli-formations (frequently a conglomerate lies at the bottom); 

 after that follow deeper-sea-formations, and, finally, come other 

 beach formations. The term Trias suits well, therefore, in reality, 

 for them all. The first who has called attention to this remark- 

 able triple division of the formations is, so far as I know, 

 Eaton. Subsequently, it has been treated of by J. S. Newberry 

 in his Memoir: Circles of Deposition in American Sedimentary 

 Rocks (Proceed. Amer. Assoc. 1873, vol. XXII, p 185), Hud 

 (Transact. Geol. Soc. Glasgow, 1868, III, part 1, p. 39); viefe - 

 also A. GeiHe's Textbook of Geology, p. 498, where still further 

 references to the literature of the subject may be found. Prin- 

 cipal Daivson calls those periods „cycles" and he gives in his „Story 

 of the Earth and Man" the following cycles of this kind: 1) Camb- 

 rian, 2) Lower Silurian, 3) Upper Silurian, 4) Devonian, 5) Car- 

 boniferous, 6) Permian, 7) Triassic, 8) Lower Jurassic, 9) Middle 

 Jurassic, 10) Upper Jurassic, 11) Cretaceous and 12) Tertiary. 1 

 It is seen therefore that those cycles are periods of long dura- 

 tion : each of them has certainly lasted for hundreds of thousands 

 of years; and in the middle of each of the cycles the great 

 transgressions of the seas have reached their maximum point. 

 The cycles are separated by continental periods. During the 

 upheaval of the dry land the position of the level beds became 

 frequently disturbed, causing the beds of the new cycle to He 

 unconformably on the top of the older one. 



The development has in that manner proceeded, at any rate 

 in the northern hemisphere. MojsLwic*. Suets and others have 

 laid stress on the fact that it has proceeded at the same time, 

 in one direction both in Europe, Asia and North America. These 

 great changes have taken place over the entire Northern Hemi- 

 sphere, and they have always had the same direction on both 

 sides of the oceans. And the same geologists have rightly 

 accentuated that this law is one of the most remarkable results 

 of geological investigation. 



