The Glacial Theory of Prof. Agassiz. 365 



vennes are probably a third ; and the Pyrenees a fourth. We have 

 one of vast magnitude in the Scandinavian mountains, whose travelled 

 blocks are found scattered over northern Europe, from the shores of 

 England to Moscow. In this country Agassiz considers the Grampians, 

 the Cumberland mountains, and those of Wales, as centres of dispersion. 



There is a question arising out the theory, which he has not touched 

 upon. If we suppose the region from the 35th parallel to the north 

 pole to be invested with a coat of ice thick enough to reach the sum- 

 mits of Jura, that is, about 5000 French feet, or one English mile in 

 height, it is evident that the abstraction of such a quantity of water 

 from the ocean would materially affect its depth. The area of the 

 space extending 55 degrees on each side of the pole, is pretty correctly 

 two-sevenths of the whole surface of the globe. Supposing two-thirds 

 of this space to be dry land, and the spongy coat of ice equal to two- 

 thirds of its bulk of water, and assuming, what is pretty near the truth, 

 that the sea occupies three-fourths of the surface of the globe, we find 

 that the abstraction of the water necessary to form the said coat of ice, 

 would depress the ocean about 800 feet. Admitting further, that one- 

 eighth of the fluid yet remains locked up in the existing polar ices, it 

 follows that the dissolution of the portion which has disappeared would 

 raise the ocean nearly 700 feet. The only very uncertain element 

 here is the depth of the ice ; but even if this should be reduced one- 

 half, we would still have an agent capable of producing a change of 

 350 feet on the level of the sea. We are besides leaving out of view 

 the southern polar region, which it is now known embraces a great 

 extent of land. If this was also covered with ice, the change would 

 be much greater than we have assumed. 



These very original and ingenious speculations of Professor Agassiz 

 must be held for the present to be under trial. They have been deduced 

 from a limited number of facts observed by himself and others, and 

 skilfully generalized ; but they cannot be considered as fully estab- 

 lished till they have been brought to the test of observation in distant 

 parts of the world, and under a great variety of circumstances. Suppo- 

 sing the theory to be substantially sound, the magnitude of the conse- 

 quences it involves will undoubtedly bring objections to light, which may 

 render modifications necessary, both in its principles and its details. 

 In the mean time, it assists us in resolving some difficulties. It contri- 

 butes, in a greater or less extent, to explain the dispersion of erratic 

 blocks, the bizarre situations they occasionally occupy, the banks of 

 clay and gravel found on the sides and at the mouths of valleys, the 

 stricB, polishing and grooving, observed on the surface of rocks in situ, 

 and of large stones in the till ; and it promises to throw light on v/hat 

 is at present a very obscure subject, the origin of the older and newer 

 alluvium. 



