( 471 ) 
water and ice, could not do much more than neutralize the influence 
of the subsidence. 
In the interglacial periods with their drier climate the mtluence ot 
the sinking was decidedly very marked again. Thus Lori^ 1 ) succeeded 
in showing that, in the interglacial period which succeeded the great 
(Riss) glacial epoch, thus previous to the last great period of extension 
of the pleistocene glaciers, the effect of the subsidence was greater than 
the counterbalancing effect caused by the accumulation of sediments. 
The northwestern and western part of the Netherlands was then partly 
flooded by the sea, and in a gulf the strata of the so-called Eem- 
system, a shallow-water and shore formation were deposited. But 
then the influence of the sedimentation compared with that of the 
subsidence became stronger again; riversand again covered the sea- 
clay of the Eem-system, the sea was forced back again, and rows 
of dunes originated successively further and further to the West an 
Northwest far out in the sea as compared with the present shore. But 
the sinking continued; the strip of land lying inside the dunes was 
flooded by the sea and covered with water. Holland was for a great 
part converted into a lagoon or “halfMore than once the water in 
the lagoon, probably during short intervals of contrary movement, 
became shallow, brackish and finally fresh enough to be filled up 
with a peat-vegetation. Then the sinking of the ground increased 
again, and sea-clay covered the peat once more. Almost everywhere 
in South-Holland and North-Holland these old peat deposits are touna 
under the blue sea-clay, generally at about 12 m. below A.P., sometimes 
at greater depth, e.g. at 19 M. below A. P. at Ummden and 
between Hoorn and Zaandam. Probably the origin of the natural gas, 
which is used for illuminating purposes in many farmhouses in 
North-Holland and South-Holland, is to be found in these deep peat- 
deposits under the sea-clay. Our knowledge, however, of these deep 
peat-deposits and the natural gas is still very imperfect. 
Perhaps it is to be recommended to fix the beginning of the 
holocene or recent period in the latter part of the lagoon stage. In 
the first, pre-historic part of the holocene the dunes extended a good 
distance further sea-ward than now, but the considerable destruction 
of the coast line by the action of the waves (only after the Pas de 
Calais was formed, probably at the end of the pleistocene, the destructive 
effect of the sea became very powerful) made them decrease rapidly, 
just as is still the case at present. The lagoon was filled with sea-water 
down to a depth of about fi meters. As Ponte has shown a short 
period of upheaval amounting to about 6 meters, followed, which 
l ) See Jomkr’s list N«. 725. 
