Eev. J. Brodie on Level Terraces, 339 
the wind, the level can be easily traced. The shingle either 
remains altogether bare, or is covered with only a few inches 
of sandy soil. When, along with the gravel, there is a small 
quantity of sand, not sufficient to bury beneath it the grass 
and other plants that grow in such situations, we find, it may 
be, several feet of soil covering the shingle and forming a 
surface, which may be termed level, though the uniformity 
be broken by a number of small irregularities. When the 
quantity of sand is great, it is formed by the force of the 
wind into hillocks of considerable height, and is sometimes 
spread over a large extent of ground. Tradition, for ex- 
ample, says that the sand thrown up by the sea in one terrible 
storm on the coast of Aberdeenshire, was so great that, 
when afterwards drifted by the wind, it covered over a 
whole parish in the neighbourhood of Slains. A great pro- 
portion of what are called downs in England and linhs in 
Scotland seem to have been formed in this manner. They 
are terraces thrown up by the advancing billow, and after- 
wards covered by a varying depth of sand. In estuaries 
the material thrown up consists principally of mud, which 
hardens when dry, and is not so readily blown about by the 
wind. After it has been thrown up it settles down upon the 
roots of whatever plants may be growing on the shore, 
and promotes their increase. By this means it is evenly 
spread over the surface, and forms the rich alluvial soil 
which we sometimes find on the plains that border the 
mouths of rivers. The lower terraces formed under the 
water by the retreating wave do not in general possess a 
horizontality of surface so distinctly marked as that which 
we find in those that are formed above high-water mark by 
the advancing billow. There is no doubt that the agency 
of the waves, if it acted alone, would produce a level plat- 
form below the water, as well as one above it ; but wherever 
there are currents, the material, carried into the deeper 
water by the retreating wave, is swept before them, and 
thrown up into banks of very irregular height. In lakes and 
seas, where there is neither stream nor tide, and in land- 
locked gulfs, where the movements usually found in the 
ocean have little influence, a level terrace under the water 
