4 



A. BLYTT. 



[No. I- 



After I had attempted to show, in a series of Memoirs on 

 the distribution of plants, the peat mosses, the old beach-lines, the 

 terraces, and the series of moraines, that climate is subject to 

 periodical alterations; I published a Paper, (Chria. Vid Selsk. 

 Forh. 1883 No. 9, translated in Biolog. Centralbl. Erlangen 1883 

 no. 14—15): On the Alternation of Strata and its probable 

 importance in the Computation of Geological Time and the Study 

 of the Changes of Species. The essential contents of that Paper, 

 so far as concerns the problem of geological time, were as 

 follows: 



Alternation of strata, by which is to be understood an al- 

 ternation of geological beds of different natures, may be pro- 

 duced by rapid temporary changes in the local relations, with- 

 out the aid of general and more permanent causes. 



But causes of the last-named kind also exist, which produce 

 alternation of beds. Two such periodically active causes may 

 be traced in the series of geological beds; one short one, re- 

 turning at somewhat regular intervals, and another longer and 

 more irregular one. The firstnamed produces an alternation of 

 the climate, as the velocity of the ocean currents throughout 

 thousands of years is supposed to increase and diminish alter- 

 nately; the last named, longer period, produces a rise and tall 

 of the sea in relation to the land, and an alternation of deep-sea 

 formations with littoral formations or fresh-water beds. The 

 supposition is expressed that those periods, traceable through the 

 series of beds, may possibly stand in connection with the two 

 cosmic periods discovered in astronomical science, the precession 

 of the equinoxes, and the changes in the eccentricity of the 

 Earth's orbit; but the Paper referred to does not attempt to 

 show in what manner such a connection arises. Whit the aid of 

 these two hypotheses, however, a factitious series of beds may be 

 constructed, and it appears that such a series, containing no less 

 than 37 alternations of strata, may again by recognized, layer 

 by layer, in the Tertiary formations of the basin of Paris. 



This result encourages still further to test the correctness 

 of the two suppositions. In regard to precession the attempt is 



