History Files





Witness Hills: Key to the Geological Past

by M Soenen & J L Putman

At the current hill zone, the sedimentation of a packet of marine sand and clay layers took 66 million years to form (the Tertiary era). This was followed by a continental degradation phase in the last 2.5 million years (the Quaternary Ice Ages - Pleistocene). Strong river erosion - with land rise and low sea level stands during the glacial periods - cleared about 100 metres of the packet, while the terrain was covered by aeolian deposits of sandy loam and loam.

After the late glacial, the erosive effect was greatly reduced (Quaternary - Holocene). At present, only a series of lined hills offer a glimpse of the sea-built pedestal.

The geological and topographical framework
Photo © Geopunt.be

The geological and topographical framework.

Large quarries in the Cassel-Kemmelberg hill zone with a broad overview of the geological structure have disappeared. They generally presented an incomplete stratigraphic sequence of the rock layers, missing both top and base layers of the hill range. Smaller exploits were limited to the iron sandstone banks in Diestian which crowns the hills, and the lower lying Eocene sands.

Mont des Récollets sand quarry (Cassel, France)
Photo © IRIS, Université de Lille

Mont des Récollets sand quarry (Cassel, France), early twentieth century: BR = Brussels Formation; LD = Lede Formation; ASS = Maldegem Formation - Asse Member; 1 = Sandstone bank BR; 2 = Basic gravel LD; 3 = Bank with large Cerithium shells; 4 = Bank with Nautilus Burtini shells

Despite the extensive erosion, the entire layer sequence has been preserved at the height of the hill tops. The spatial pattern of the overlying Diestian has so far been interpreted as tracing back to an old sandbank complex, bound to a coastal zone. The grains of the Diestian sands were afterwards, at emersion, sintered together by a ferruginous binder to iron sandstone levels.

Diestian conglomerate
Photo © Philippe Vercoutter

Diestian conglomerate.

Pebbles, locally enclosed or not, originally being silex tubers from chalk layers later rounded to pebbles during transportation in the water, can be found loose in the sands or fixated to conglomerate in the iron sandstone. Where these occurred in the erosion-protected area containing iron sandstone, the hills in the underlying layers were sculpted in the Pleistocene.

Relief in the Kemmelberg zone
Photo © P Diriken, Georeto, & W Willems

Relief in the Kemmelberg zone.

It is true that this actually prevalent theory is questioned by geologists, and a change of name for the Diestian cannot be ruled out. The geological structure of sub-horizontal rock layers, descending to the north, determines the location of sources on the contact of sand and clay.

The transition zone from sandy loam in the north to a loam mantle in the Douve Valley coincides with the line of the hill tops on which, as a result of erosion, the tertiary subsoil outcrops. Other Quaternary deposits cover the terrain slopes with colluvium or have filled the valley bottoms of the Douve and Leie, which are visible as sedimentation reliefs.

Loam bottom in the Douve valley
Photo © J L Putman

Loam bottom in the Douve valley. Diestian tops from Scherpenberg and Kemmelberg.

In contrast to the lower zones covered with sandy loam and loam, which were cultivated where possible, the sandy Kemmelberg plateau was deprived of many agricultural possibilities. Nevertheless, the Diestian top layer has been anthropogenically disturbed to a depth of several metres over large areas.

The disturbances are diverse in origin: Neolithic settlement traces, rampart and ditch construction in the Iron Age, iron sandstone quarrying, grenade impacts and trenches from the First World War or Second World War, archaeological excavations, etc.

Gully carved in the iron sandstone bank (Iron Age Kemmelberg)
Photo © A Van Doorselaer, RAMS

Gully carved in the iron sandstone bank (Iron Age Kemmelberg).

In addition, a geological scar left its mark on the plateau rim. A landslide, presumably in the aftermath of the ice ages, resulted in a steep rim as a northern boundary.

Kemmelberg, steep rim
Photo © J L Putman

Kemmelberg, the steep rim.



Text copyright © Archeo Kemmelberg. An original feature for the History Files: Kemmelberg.