154 DK. J. MOKISON ICE AK^D ITS WOEK. 



shire. If this he the case the stone probably comes from no great 

 distance, and must be looked upon as the remnant of an Eocene 

 bed, which formerly covered this part of the country, and not as 

 a true erratic boulder. A boulder of about the same size, but 

 much more angular in form, may be seen just inside the wall of 

 St. Stephen's churchyard, close to St. Albans. This boulder consists 

 of a rather coarse sandstone probably of Carboniferous age. There 

 are also many masses of conglomerate scattered about the country, 

 some of them of very considerable size, but they must be con- 

 sidered as remnants of a disintegrated local bed, and not as 

 boulders in the true sense of the word. 



Another proof of the former existence of a glacial period is 

 found in the Boulder-clay or Till which covers wide areas in 

 Scotland and the greater part of England and Ireland. This is 

 generally a tough, tenacious clay, occasionally, however, more or 

 less sandy, and full of stones varying in size from mere grit or 

 pebbles to blocks several feet, or, it may be, yards in diameter, which 

 are scattered irregularly through it. Sometimes the stones are so 

 numerous that hardly any clay is visible, and sometimes they are 

 comparatively few in number, so that the clay can be used for 

 brick-making. These stones are of a peculiar shape, somewhat 

 angular in form, but the sharp comers and edges are generally 

 more or less smoothed away, so as to render them sub-angular. 

 Many of them are perfectly smoothed and polished, and covered 

 with scratches or striae of varying degrees of fineness. These striae 

 are better seen in the hard limestones or igneous rocks than in 

 those of sandstone or other comparatively soft material. The 

 majority of the stones seem to be fi'agments of rocks in the im- 

 mediate neighbourhood. In Chalk districts such as this the boulder- 

 clay is often full of lumps of chalk ; in the neighbourhood of the 

 Coal Measures of pieces of coal. Mixed, however, with these local 

 stones are boulders of rock foreign to the neighbourhood, which 

 must have travelled considerable distances. In some places marine 

 shells, more or less fragmentary, of a northern or Arctic type, are 

 found in the boulder-clay. In other places bones of the mammoth, 

 the reindeer, and other animals are found. 



Boulder-clay is not a continuous deposit, but often contains 

 irregular patches and layers of sand and gravel, and in some places 

 thin beds of peat, trunks of trees, and other remains of land-vege- 

 tation. If a layer of boulder-clay be removed from the underlying 

 rock, the latter is often seen to be smoothed, polished, and striated, 

 or if the rock be of a soft material it may be much broken up and 

 disintegrated. Boulder-clay covers a great part of the Lowlands of 

 Scotland and Ireland, and also extensive areas in England, 

 particularly in the north and east. It extends over the greater 

 part of the eastern division of Hertfordshire. 



In this neighbourhood we find a mass of boulder-clay at Bricket 

 Wood, where, containing comparatively few stones, it is used for 

 brick-making. Here the clay is of a somewhat mottled appearance, 

 being very light-coloured in places owing to the large quantity of 



