364 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



Thus, then, according to the elaborate investigations of the Swedish 

 Survey, that region has passed through a cycle of geological phenomena of 

 a somewhat complicated charactei", but in regard to the general order of 

 which there can be no doubt. We have, first, a period of glaciation, when 

 the land was higher than it now is and largely covered with ice, which made 

 its way down the declivities, striating and polishing the rocks, carrying 

 detritus to lower levels, and, with the aid of the torrents of water melted 

 from the glacial masses during the long northern summer, depositing it 

 irregularly over the surface. 



To this first period succeeded an epoch of depression of the land, accom- 

 panied by a general shrinking of the ice fields. As the surface by its sinking 

 was brought into a position to be acted on by the sea, the detrital material 

 previously irregularly scattered over it as left by the ice sheet was worked 

 over and rearranged, the finer clayey portions being carried off" and 

 deposited in a stratified form at some distance, the coarser left on the shore 

 forming long lines of water-worn boulders or asar. At this time icebergs 

 were also doing their share of the work in transporting detrital materials to 

 greater or less distances, depositing a portion of them over Central Russia 

 and Northern Germany. 



The third epoch was that in which the Scandinavian land mass rose again 

 from the water, gradually assiuning the outline which it now has, the Baltic 

 Sea becoming closed on the north, while a narrow passage connected it on the 

 south with the German Ocean. During this period tlie various previously ex- 

 isting detrital deposits received farther modifications, such as would necessarily 

 result from the action of the ocean waves and currents on loose materials 

 lying upon a sloping surface and gradually brought by the rising of the land 

 into such a position as to be subjected to their influence. Moreover, as a larger 

 area became lifted above the water the size of the rivers increased accord- 

 ingly, and fluviatile action became more and more conspicuous, exercising an 

 important effect in modifying the form of the previously existing detrital 

 deposits. Thus, by degrees, the surface of the land attained its present con- 

 dition, with its great variety of gravel and clay deposits, the former being 

 collected in considerable part in the form of ridges parallel with the coast 

 line, while the latter are widely spread over the surface, especially in the 

 southeastern portion of the Peninsula, whence they have been distributed in 

 part through the river valleys by subsequent fluviatile action. 



When we endeavor to follow the course of events during the Glacial 



