488 A. Blytt on the probable Cause of 



have pointed out that it has taken place simultaneously in the 

 same direction in Europe, Asia, and North America. These 

 great changes have taken place over the whole of the northern 

 hemisphere, and on both sides of the oceans they have con- 

 stantly had the same direction. And the same geologists 

 have justly insisted that this law is one of the most remark- 

 able results of geological investigations. 



The development of organic life, as we now know, has 

 gone on uninterruptedly from the earliest times. There has 

 certainly never been any general destruction, never any com- 

 pletely new creation. The new has developed from the old 

 through transitional forms and in the course of millions of 

 years. If we knew all the deposits which have been formed 

 it would be impossible to draw any boundaries between geo- 

 logical formations. One would imperceptibly pass over into 

 the other. The boundaries between formations correspond 

 with great gaps in the series of beds. In the time which 

 intervened between the youngest bed in an older and the 

 oldest in a younger cycle, the land in the northern hemi- 

 sphere lay so high that no marine deposits were formed in the 

 parts of the earth's crust which are accessible to our investi- 

 gations. Nevertheless the development of living forms went 

 on its even course. But when, after a long time, the land 

 was again submerged, the life in the sea had changed, and 

 beds with new fossils were deposited upon the old ones. And 

 it is from the animal remains of marine deposits that the form- 

 ations are determined. Hence the sudden chanoe of fossils 

 where a new formation commences is not due to anv catas- 

 trophe, but simply to a shorter or longer interruption in the 

 formation of deposits in the parts of the earth which we are 

 able to examine. There is no doubt that there are transition- 

 beds between formations, but they lie concealed from us at 

 the bottom of the sea. It is only in certain strongly plicated 

 chains that these beds are upheaved and can be examined. 

 Thus in the Alps there are transitional beds between the 

 Cretaceous and Tertiary, between the Permian and Trias, &c.* 



* "As long ago as 1846, Darwin, in his observations in South America, 

 showed that certain assemblages of fossils presented a blending of cha- 

 racters which are of Jurassic and Cretaceous age respectively. Since 

 that date, the study of the fossil faunas of South Africa, India, Australia, 

 New Zealand, and the Western Territories of North America has fur- 

 nished an abundance of facts of the same kind, showing that no classifi- 

 cation of geological periods can possibly be of world-wide application " 

 (J. W. Judd, Presidential Address to the Geological Society, 1888, and 

 'Nature,' March 1, 1888, p. 426). See also 'Mo]sis,o\i\.cs, Die Dolomitriffe 

 Siidtirols und Veneliens, ^'ienna, 1879, p. 36 ; and von Hauer, Die 

 Geoloffie, Vienna, 1875, p. 515. 



