198 OUTLINES OF FIELD-GEOLOGY PARTI 



of mammalia. The wild oxen and deer of the time 

 of the lakes and early morasses have often left their 

 remains at the bottom of the mosses. Human i 

 ought also to be looked for. Canoes and stone imple- 

 ments are often taken out of peat deposits. Stockaded 

 islets or crannoges may likewise now and then be found. 

 It is always desirable to enlist the co-operation of the 

 workpeople at such places, as they are far more likely 

 than an occasional visitor to come upon objects of 

 interest. 



Brick-earth. Where a thick deposit of loam or earth 

 covers the surface, especially on the slopes of broad river- 

 valleys, attention should be directed to its composition 

 and contents. If it contains occasional land-shells, is 

 not very well stratified, shows no lines of gravel, nor any 

 water-worn stones, and has never yielded either a lacus- 

 trine, fluviatile, or marine shell, it may be presumed to 

 be a subaerial formation due to the long-continued action 

 of rain or wind, gently moving the soil down to the lower 

 grounds. In the lower parts of the valley of the river 

 Thames thick accumulations of this kind occur, and their 

 antiquity is indicated by the peculiar assemblage of ex- 

 tinct mammalia, including forms of elephant, rhinoceros, 

 and hippopotamus, which they contain. 



River Terraces. These conspicuous features of most 

 river valleys can be easily traced along either side. The 

 observer ascertains the number of terraces (in the valleys 

 of British rivers there are commonly three), also their 

 general average height above each other and above the pre- 

 sent mean level of the river. He compares the character 

 of their deposits, and seeks for any information thence 



