HOW GLACIERS HAVE CONTRIBUTED TO SEA-BOTTOMS. 
539 
elapsed before such shelly marine remains were discovered in the central counties 
of England, and reminding our readers that Russia has, as yet, been very little ex- 
amined, we have no doubt that additional similar proofs will be hereafter obtained 
in it. But even should such be more extensively discovered, they may, after all, prove 
exceptions to the general rule, and we found this opinion upon the very nature of 
the prominent masses of the detritus and our idea of its origin. Those portions of it 
which were formed by powerful currents dependent on upheavals and depressions 
cannot be expected to contain sea shells. Still less could the glaciers which we have 
supposed to exist formerly in Scandinavia have contained marine exuviae, for, as 
in the Alps and similar centres, they must have been chiefly charged with blocks, 
gravel, mud and sand. The portions of masses thus originally constituted being 
floated to southern tracts and melted, would cover over the bottoms of seas with 
thin, irregularly heaped-up materials, and thus can we explain why such deposits, 
though becoming truly submarine, should rarely, if ever appear in conjunction with 
sea shells, — ice, if we may so express ourselves, having been the chief agent by 
which a subaerial impress has been given to large portions of the bottom of the 
ocean. 
