102 [P roc . B.N.F.C., 



lies above the earlier deposited and more solid strata. As already- 

 mentioned, it may easily be known by its want of stratification. 

 It may be unnecessary for me to inform such an audience as this, 

 that sediments, whether of mud, sand, or gravel, deposited in 

 water, always occur in regular layers, one above another. Further, 

 water always sorts the material which it holds in suspension. A river 

 conveying mud, sand, and pebbles seaward, parts with the heavier 

 pebbles first, the sand next, and conveys the mud for a consider- 

 able distance into the sea. On the other hand, a glacier, where 

 it melts off, precipitates the stony and earthy matter that had 

 fallen on its surface from the cliffs along its margin, in irregular 

 heaps, called moraines > which are utterly devoid of stratification or 

 arrangement. For the same reason, when a glacier in a country 

 like Greenland reaches the coast, and is projected over a cliff, 

 until a portion breaks by its own weight and floats off as an ice- 

 berg, the earthy matters contained in such ice-mountains are depo- 

 sited in the sea bottom when the iceberg melts. It is believed 

 that such accumulations would in most cases be devoid of stratifi- 

 cation. The resemblance between the drift deposits and the mo- 

 raines of glaciers first led Agassiz, who had an opportunity of 

 studying their structure in his native country, Switzerland, to pro- 

 pound the theory that these accumulations were formed by ice, 

 and not by water, as had been formerly supposed. 



But there are other proofs of the former presence of an ice cap 

 in these and other northern countries. Many of the boulders are 

 scratched and polished, similar markings being found abundantly 

 in the rocks over which the glacier passed. These markings were 

 well seen by the section of the British Association which visited the 

 Castle Espie quarries in August last. This quarry is covered by a 

 deposit of boulder clay 40 to 50 feet thick. Many of the boulders 

 are ice scratched, and the upper layer of limestone is polished 

 and striated. In the valleys of Switzerland, occupied by 

 glaciers, similar phenomena occur. The boulders found in the 

 moraines are scratched, and the rocks over which former exten- 

 sions of the glaciers passed are scratched and polished. Further, 



