202 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



drift is distributed in the form of long sand-banks, "^rmwees," or ^'•osar^' 

 as they are called in Sweden, often of great length and breadth, and 

 rising sometimes more than 100 feet above the depressions between 

 them, which last are occasionally of great width. These trainees 

 are often composed of finely laminated sand and clay, containing 

 shells identical in species with those now living in the Baltic or in 

 the northern seas ; they traverse, from the shores of the Baltic, the 

 Silurian, Devonian, and carboniferous regions in succession, de- 

 riving new materials from each zone of rocks crossed, but always 

 indicating a southerly direction of the drift, the Devonian detritus 

 never being found in the Silurian zone, nor the carboniferous in the 

 Devonian zone. 



Mr. Forchhammer describes the boulder formation of Denmark 

 as being of different ages. The oldest which affords any distinct 

 evidence to mark its age consists of a congeries of clays, marls, and 

 sands, which have been traced to a depth of several hundred feet, 

 and contain boulders throughout the entire mass, extending to the 

 deepest part of the series. The boulders, sometimes several hundred 

 cubic feet in size, are of granite, gneiss, porphyry, greenstone, and 

 quartz rock, and also of transition (Silurian) sedimentary rocks ; 

 none of these occurring nearer than Norway and Sweden. Besides 

 these travelled blocks, there are many parts of the formation com- 

 posed of chalk, identical with rocks upon or near to which the 

 boulder formation occurs. In the duchy of Schleswig, this boulder 

 formation alternates with beds of Brown Coal, a deposit which ex- 

 tends over the greater part of Denmark, and which, besides brown 

 coal, consists of clays, limestones and sandstones, containing fossils 

 that in the opinion of Mr. Forchhammer mark it to be identical 

 with the sub-Apennine group. The causes which produced this 

 boulder formation, in part at least, were therefore in operation as 

 early as the Miocene tertiary period (if, as some maintain, the sub- 

 Apennines are of that age), during which the sea, overspread at its 

 bottom by this detritus, was inhabited by Mediterranean species. 

 There is clear evidence in the works of the authors I have quoted, 

 of the operation of the same causes long after the northern seas 

 were inhabited by existing species ; and throughout the whole of 

 this period, how long we have no means of determining, all the 

 land in Northern Europe overspread by the boulder formation must 

 have been under the sea. Thus the authors of the ' Geology of 

 Russia ' describe the deposit of recent shells in the valley of the 

 Dwina, 150 miles inland from Archangel, as covered by sand and 

 gravel, which, they say, they would have great difficulty in sepa- 

 rating from the superficial northern drift; and they add, that "a 

 recent excursion through Sweden has convinced them that in the 

 neighbourhood of Upsala, marine post-pliocene deposits, containing 

 the Tellina Baltica, are there covered by coarse gravel and large 

 erratic blocks, as stated by Mr. Lyell." 



The ingenious and ardent naturalists of Switzerland, who have 

 held that the boulder formations of Northern Europe were produced 

 by sub-aerial glaciers, never could have advanced so extravagant a 



