Cruise and Symonds on Belgian Bone-caves. 569 



that either engulfed streams, or the action of waves, affected the interior 

 of the caves precisely as was observed by Sir C. Lyell and myself in 

 the caves of Gower and St. Asaph. Although encrusted with stalactitic 

 matter there are numerous pot-holes and marks of water action. 



Thirdly. Along the valley of the Lesse there have been undoubtedly 

 physical changes in the configuration of the district since the depo- 

 sition of all the stratified deposits within the caves. This is also 

 what we know has occurred, in many instances, among the subter- 

 ranean caverns which contain the bones of the extinct mammalia and 

 the flint implements in England. ' 



Fourthly. It is the opinion of Dr. Dupont, if we rightly compre- 

 hended him, that the " Loess," which underlies the stalagmite of the 

 caverns, and consists of stiff clay and well stratified sands — the same 

 which contained the human jaw and the bones of the lihinoceros 

 tichorhinus — is of marine origin. I do not know what reasons Dr. 

 Dupont has for holding this opinion, but we shall soon be made 

 acquainted with them, as that gentleman is about to publish a work 

 upon the physical geology as well as the animal contents of these 

 Belgian caves. This is an important point, for if the basement 

 gravel and silts in the caverns turn out to be marine, I see no way of 

 escaping from the conclusion that the valley of the Lesse was sub- 

 merged beneath the waters that deposited the pebble and drift beds 

 on the summit of the limestone platform that rises above the caverns ; 

 and consequently that these cavern drifts are pre-glacial. We arrived 

 at other conclusions, upon which however I am imwilling to lay 

 much stress, as our survey was necessarily short. It appears from 

 the statements I gathered from Dr. Dupont, that on the flanks of the 

 Lesse valley, above the bone caverns, but below the platform drifts, 

 there are high-level valley gravels which teU of an ancient river which 

 flowed at a far higher level than the waters of the existing river, and 

 which old river is not unlikely to have washed down pebbles and 

 drifts derived through streams by lateral som-ces, from the platform 

 drifts on the high country around. Again the pebble-beds which 

 lie at the base of the deposits of the " Trou des Nutons " and the 

 " Trou de Naulette " do not appear to me to have a marine aspect, 

 they have the arrangement of an old river shingle. My own im- 

 pression is that tliis shingle was derived from the platform drifts on 

 the upper sm-face of the country, and was washed into the caverns by 

 the agency of the underground streams which opened out into the 

 valley of the ancient Lesse. This is supported by the evidence of the 

 animal remains found in the basement deposits. Eemains of the 

 heaver were found by Dr. Dupont, and this testifies more to fresh- 

 water conditions than marine. Again we believe that the " Loess," 

 or stratified clay and silt which contained the human jaw and mam- 

 malian bones, is a fluviatile silt, the deposit of waters which once 

 swept into or through the caves before those relative changes of 

 land and water level were brought about, which caused the floodings 

 by turbid waters to cease, and the floor of the caves to become dry 

 land, and the stalagmite to gather above the human and animal relics 

 with its encrustiag seal. 



