316 Horner's Geological Address. 



ter being usually angular, the materials of the former being 

 rounded and worn by attrition. It appears to me to have 

 been clearly proved, that the boulder formation is not the 

 work of a sudden transient action of short duration, but the 

 result of operations that were going on during the middle 

 tertiary deposites, and, in Europe, extended at least to the 

 Pleistocene period ; that the greater part of the accumula- 

 tions took place since existing species of testacea inhabited 

 the adjoining seas ; and that the transport of erratic blocks 

 took place at a later period. It seems to be no less clearly 

 established, that the boulder and drift accumulations and the 

 erratic blocks now covering the dry land, were deposited upon 

 a sea-bottom, which has been since upraised. Where the 

 smaller detritus and rounded boulders came from, and how 

 they were drifted into their present situations, are branches 

 of the subject involved in great obscurity. That fragments 

 of hard rock were the tools which grooved the furrows and 

 striae, and polished the surfaces of hard rocks they passed 

 over, is pretty evident ; but what held and guided the tool, 

 what force applied it, to what extent ice, and to what extent 

 water, was the agent, is not so clear : that both have acted, 

 there can be no doubt. It is, I think, very satisfactorily 

 shewn, that the erratic blocks must have been brought down 

 from lofty mountains, to the open sea that washed their bases, 

 by glaciers ; that they were floated to great distances by 

 masses of ice breaking off from these glaciers, to form ice- 

 bergs, in different directions from central points, and stranded 

 on elevated parts of the searbottom, without having been sub- 

 ject to much attrition ; and, moreover, that these erratic blocks 

 can, in a great number of instances, be traced to their parent 

 rock, though now separated some hundred miles. Some of 

 the evidence in support of these positions, supplied during 

 the last year, I will now bring forward. I regret that my 

 limits will not allow me to do greater justice to the authors 

 to whom we are indebted for it, either as regards their facts, 

 or their deductions from these facts. 



The boulder formation and erratic blocks cover an enormous 

 area, from the Arctic Sea over a great part of Northern 

 Europe ; not continuously, but often uninterruptedly over vast 



