20 WALKS AND TALKS. 



feet deep, without reaching bed-rock. Those who have seen 

 such wells have observed the deeper structure of the Drift ; 

 and they report it much like what we see in the gravel-pit, I 

 will tell you how we shall ascertain the arrangement to the 

 depth of perhaps two hundred feet. Go to the lake-shore, or 

 the sea-shore. Of course it must be a place where the shore 

 is not formed of bed-rocks. Here the whole thickness of the 

 Drift may be cut through, exposing at the bottom the solid 

 foundation on which the Drift reposes. Well, here we find 

 two kinds of Drift. The semi-stratified Drift passes down 

 into a sheet of Drift quite unstratified. It consists of blue 

 clay and a large quantity of imbedded bowlders. These are 

 rounded like those at the surface. They are in every respect 

 the same thing made, apparently, by the same agency; trans- 

 ported in the same company. This is the Bowlder Clay 

 or Till. 



We must state, however, that in some situations the semi- 

 stratified Drift rests directly on the bed-rock. Perhaps in 

 these places the Bowlder Clay was washed off before the semi- 

 stratified Drift was laid down. Again, there are many places 

 where the semi-stratified Drift does not rest on the Bowlder 

 Clay perhaps because it was never laid down ; but more 

 probably because it has been removed. In such places the 

 stiff, blue clay is exposed over the surface, and the soil is full 

 of bowlders. Can you not call to mind such a place? 



The sheets of sand and gravel, often obliquely laminated, 

 which we saw in the gravel-pit, were there cut through in a 

 vertical section presented edgewise. You must think of these 

 sheets as extending into the earth a certain distance, but very 

 i ilar in extent as well as in form and position. Some 

 of them are flat; some are concave upwards, and some are 

 convex. Now and then one is nearly horizontal, but most are 

 considerably inclined. 



Did you ever see a huge mound of rock-rubbish at the 

 foot of a torrent rushing down a steep ravine to the open, 

 level land a torrent sometimes suddenly swollrn to a t< nitic 

 and maddened volume, which tears stones and trees from thrir 



