142 
parts of the world — in high, if not in low, latitudes — I would 
remark that many American geologists have lately found it 
difficult to explain all the phenomena presented by the 
enormous accumulations of boulder-drifts exposed by the 
railroads of British IN^orth America without coming back to 
the theory they now believe they too hastily rejected, 
namely, that, during the breaking up of the glacial con- 
ditions of the northern hemisphere, marine aqueous action 
acquired an intensity which, so far as we know, has not 
since been paralleled. 
5. Irregular Terraces in Drift. — In the West Riding of 
Yorkshire, as well as in nearly every part of England and 
Wales, there are innumerable small terraces. The most 
striking I have seen are in the neighbourhood of Spofforth, 
Settle, and Malham (see plates). The last are the most worthy 
of consideration. They are chiefly in the yellowish-brown 
drift, but I have no doubt that in some places they are 
wrought into the solid rock. They may be seen on the east 
side of the Aire valley up to a great height above the river, 
both on steep slopes and on slopes at an angle of only two or 
three degrees. They are very seldom horizontal, but dip with 
the hollows and rise with the ridges. They generally present 
a rude parallelism, but are never perfectty regular. They con- 
form to the longitudinal contour of the ground. To the north 
of Malham they are more ridges and furrows than terraces, 
and run not along, but doivn the face of the slope. Their mode 
of occurrence shows that they were only formed along the 
face of a slope when it happened to lie in the direction of the 
moving cause. In other cases they cross slopes in ascending 
and descending order. They thin out, reappear, swell, and 
diminish. They are very similar to the vast majority (not 
all) of the terraces of the chalk districts of the south of 
England ; and in Yorkshire, as well as the south of England, 
in places where the terraces happened to approach regularity, 
