16 



A. BLYTT. 



[No. 8. 



The Challenger expedition has taiight us, that all the strati- 

 iied rocks which geologists hitherto have known even dee^ sea 

 formations must have been formed comparatively near the shore. 

 They are all of quite a different nature than the strata in 

 the abysses of the great oceans. From this follows that the 

 variations in the rain-fall might have had some influence on the 

 nature of the strata in the known geological formations since 

 they were formed comparatively near land and are the result 

 of the erosion of the solid rock. A weak river is unable to 

 carry debris far out to sea, but a strong one is capable of sup- 

 plying the sea-currents with deposits over great areas. When, 

 therefore, the rivers alternately increased and decreased, the sand, 

 clay, and gravel was carried, now far, now short into the sea, 

 and thereby the variations of the layers were produced. 



It is, however, not the intension to assert that all alternations 

 of layers are due to that long climatic period. When the stra- 

 tification goes on quickly, and the supply of matter is plentiful, 

 rapid local changes may produce an alternation of strata. In the 

 Norwegian marl-clay, formed during the melting of the inland lee 

 alternating thin layers of sand and clay are found, varying in 

 colour, sometimes only a quarter of an inch in thickness, or 

 even less. These variations must be ascribed to local changes 

 during brief spaces of time, and cannot be referred to long cli- 

 matic periods. But, of course, such layers are only formed in 

 the imraediate vicinity of the coast, and during the constant ad- 

 vance and retrogression of the latter, which may be traced 

 through all geological ages, such shore formations were most 

 exposed to destruction. They were frequently lifted above the 

 sea, and more exposed to the destructive agencies air and cur- 

 rents than those formed in deeper waters further from the shore. 

 For this reason these quickly formed layers have at all times 

 been more exposed than others to destruction, and we must al- 

 ready from that reason conclude that most of the Imjers which 

 constitute the geological stratified deposits were formed some- 

 what further from the shore, and that, consequently, the time of 

 thcir formation was longer. From the thickness of the layer 



