( 534 ) 



half-waj belweeii the last-named place aiul Tilburg, of erratics one 

 of which weighed 200 K.G. '). G. Delwaqle then again mentioned 

 two pebbles of granite fonnd in the neighbourhood of Maastricht "). 

 It is only during the last ten years that a deeper interest has been 

 taken in the study of this subject, with the result that the presence 

 of erratics of Northern origin has been ascertained in several places, 

 as we gather from the writings of C. Bamps, V. Becker, E. van den 

 Broeck, p. Cogels, E. Delvaux, G. Dewalque, A. Erens, 0. van 

 Ertborn, J. LoRiÉ, A. Renard and Ch. de la Vallee — Poussin. 



Another fact w^orthy of notice is the presence, at these very places, 

 of boulders derived from the district of the Rhine. The first indications 

 of sucli finds, by G. Dewalque, are rather questionable. They were 

 fragments of rocks from the lava of Niedermendig, near Andernach, 

 frequently met with in the valley of the Amblève, but were believed 

 to have been fragments of mill-stones, formerly used at Stavelot and 

 Maimed}'. Subsequently E. Delvaux found a few pieces of lava and 

 pumice stone in the diluvium of the Campine ') ; but it was A. Erens 

 who discovered and described a great number of rocks derived from 

 the Rhine district, composed of lava from Niedermendig, pumice 

 stone and Taunus-quartzite *). These were followed at a later 

 period by trachyte from the Drachenfels, basalt and hornblende- 

 andesite from the Siebengebirge, and melaphyre and agate from the 

 basin of the Nahe '). The discovery of these fragments in the North 

 of Limburg admits of no other interpretation than that these rocks 

 must have been carried South, simultaneously with the detritus from 

 Scandinavia. 



It cannot be denied that fewer erratics from Scandinavian rocks 

 are found South of the Rhine than North of it. We give the following 

 reasons in explanation of this fact: 1^'. During the progress of the 

 Baltic icestream in a South-Western direction, the Scandinavian drift 

 must already have lost a certain portion of its material by the mix- 

 ture of the debris of its own moraine with that of other sources; 

 2°'^. It must have suffered further loss by mixing with the moraine 



1) Bull. Soc. paléontolog. Bruxelles p. 36. (Seance du 5 Septembre 1858). 



^) Prodrome d'une description géologique de la Belgique. Bruxelles et Liége. 

 1868, p. 237. 



8) Les anciens depots de transport de la Meuse. Ann. Soc. géol. de Belgique 

 XIV. 1886-87. Mém. p. 102. 



*) Note sur les roches cristallines . . . Ann. Soc. géolog. de Belgique XVI. 1888— 

 89. Mém. p. 414, 439—441, 444. 



6) Recherches sur les formations diluviennes du sud des Pays-Bas. Archives 

 Teyler (2) III. 6''™^' parlie. Haarlem 1891. Tableaux syuuptiques I — V. 



