MECHANICAL ACTION OF GLACIERS. 161 
are also found in the large moraines of which mention has 
been made. 
_Débris of moraines cover likewise great extents of low- 
lying landsand valleys; and they there entail nosmallamount 
of labour in clearing the ground for cultivation. To obtain 
ground fit for cultivation 50 centimetres, or 20 inches, in 
depth, it is often necessary to dig out and carry away 
erratic stones which would have covered the whole area 
to a depth of a metre, or 40 inches. 
Beds of clay and banks of shells of the glacial period are 
often found spread over areas of great extent, especially 
in districts open to deposits from Silurian regions of lime- 
stone and argilaceous schists, which have been ground 
down and worn away during the glacial period. Trans- 
ported as moraine mud by the waters flowing from the 
glaciers, they have formed beds under the surface of the 
sea in these ancient times. In different places the lower 
bed of clay is limestone or marly clay ; often it is filled with 
diversely shaped lumps of hard marl, which sometimes 
enclose fossils. This marly clay has made fertile the flat 
country of Remerike and of Smaalehnene, the east part of 
the valley of Christiania, Eker, the west flat part of Ring- 
erike, Jederen, and the flat country of Drontheim. The 
marshy and peat lands of Listerland and of Jederen rest 
on a bed of marine clay. For all of this information I am 
indebted to the reports by Dr Broch and Principal Forbes ; 
and this is also the case with what follows. It is only the 
circumstance of my having neglected to mark quotations 
in MS. notes made years ago, which prevents me from 
in licating such here. 
By the fragmentary shells found in cretaceous sand, the 
succession of molluscs, both marine and those of fresh- 
waters, may be traced. For our present purpose it is 
enough to notice that by the remains of these the ground 
has been enriched. 
In going up one of the great water-courses from the sea 
towards its source we come first to a level where the 
M 
