150 M. Dumont on the Equivalents of the Cambrian 



esting, on account of the variety of the rocks, the modifica- 

 tions which they have undergone, and the dislocations of the 

 strata. 



The forest of Aix is composed of sand and of freestone be- 

 longing to the lower chalk formation ; but in advancing to- 

 wards the N.W. there successively appear chalk, the lime- 

 stone of Maestricht, and even the lower tertiary sand. 



Above these rocks a bed of the upper tertiary formation 

 extends, its base being composed of flints and its upper part 

 of alluvium. We may easily be satisfied that this layer 

 originally covered the whole country, and would still conceal 

 the subjacent rocks, but for the numerous valleys which furrow 

 it, and whose origin is consequent!}' posterior to the last ter- 

 tiary deposit. Now, all these valleys owe their origin to faults 

 and to transverse fissures connected with them. At one time 

 there has been a simple change of level among the masses 

 separated by faults, and at another time there has been an 

 unequal movement {inouvenient de bascule'] having for its 

 axis the line of a fault, which has deranged the primitive 

 horizontality of the strata. 



For instance, the mass included between the fault of the 

 valley of the Guele, and that which caused the valley in 

 which the rivulet Nysweiller flows, has been raised in com- 

 parison with the mass situated to the north of this latter fault, 

 to such a degree, that the sand of the forest of Aix occupies a 

 higher level than the chalk which stretches from Aix-la- 

 Chapelle to Wittem. 



The isolated mountain of Louisberg to the north of Aix-la- 

 Chapelle, must likewise have been raised like a plug, be- 

 cause the chalk at the summit is at a higher level than that 

 which prevails to the west of the city. 



Besides the great faults which have divided the formation 

 into large masses and changed their levels, there is an infinity 

 of small faults which have subdivided these masses and pro- 

 duced new dislocations ; so we must nearly always expect to 

 find a disagreement between the level of beds of the same 

 kind, at the two sides of a valley, or to see on one side of the 

 valley beds of a kind different from those which had be enob- 

 served on the other side. 



These observations entirely confirm what we advanced on 

 thesubject of faults in our preceding report. 



In traversing the district included between Aix-la-Chapelle 

 and Kunraad, the chalk is found to lose its earthy texture, 

 and becomes so compact that it resembles certain Jura lime- 

 stones. The Maestricht limestone also acquires a texture 

 and an aspect which makes it so difficult to recognise, that it is 



