On Altered Rocks from Bastogne. 599 



a sort of island in the Drift. At the well-known locality by the 

 lighthouse it seems to overlie a drift, but on closer examination the 

 latter appears more probably to have filled a cavity excavated in the 

 Chalk : this apparent inlier of Drift probably being only a remnant 

 of a much larger mass; therefore it is likely that this part of the 

 coast nearly corresponds with a pre-Glacial chalk-cliff against 

 which the Drift was deposited. 



In the Jasmund district the authors lay special emphasis on 

 three points: — (1) The ' inliers ' of Drift appear to occupy valleys 

 excavated in the Chalk ; (2) these valleys can be traced for some 

 distance inland ; (3) the steep walls of Chalk towards which the 

 Drift dips sharply, and against which it ends abruptly (usually on 

 the southern side), often trend gradually inland, as if the present 

 coast-line had passed obliquely across an old valley. In one or 

 two instances the Drift is slightly twisted up against this steep 

 face of Chalk. The authors call attention to cases where the Drift 

 clearly rests against old surfaces and cliffs of Chalk; and to one in 

 particular, which was not visible in 1898, where (a) clay, (b) sand, 

 and (c) clay occupy a shallow valley, and have assumed a synclinal 

 form. The authors give reasons to show that neither solution of 

 the Chalk, nor ice- thrust, nor folding, nor even faulting, can 

 satisfactorily explain the peculiar relatious of the Drift and Chalk 

 in Rtigen ; and they can find no better explanation than that offered 

 in their previous paper. 



2. ' On certain Altered Rocks from near Bastogne and their 

 Relations to others in the District.' By Catherine A. Raisin, D.Sc. 



Prof. Renard, from the petrographical study of specimens, and 

 Prof. Gosselet, after description of the district and its stratigraphy, 

 have attributed the changes in these rocks to mechanical dis- 

 turbances. Dumont had previously described many examples and 

 inclined to the view of contact-alteration, which was favoured by 

 Von Lasaulx's discovery of a granite in the Hohe Venn, and 

 M. Dupont's identification of chiastolite from Libramont. 



The present paper treats especially of the garnetiferous and 

 hornblendic rocks, giving the full petrographical and field-details 

 of a few examples. It points out that the effects of pressure are 

 evident over the whole district, while mineral modifications re- 

 sembling the results of slight contact-action are found in certain 

 areas. In a few cases these modifications are more marked, and 

 sometimes increase as we approach veins composed of quartz, felspar, 

 and mica, such as might be connected with a concealed granite. 



The peculiar garnetiferous and hornblendic rocks, although 

 occurring within the zone of alteration, are extremely limited, 

 often forming patches or bands a few feet across. They differ, as 

 described in the paper, from ordinary contact-altered rocks. The 

 evidence, in the authoress's opinion, is in favour of Prof. Bonney's 

 suggestion that they are due to some form of hot-spring action. 



