8 DR. J. W. GREGORY ON THE ' SCHISTES [Feb. 1 896, 



are continuous from the end of the Mont des Arrhets, round the Trias 

 outlier, to the crags in the valley below, where they finally plunge 

 under the main sheet of Trias. Od the northern side of this boss 

 of dolomite there is a very steep slope down to the Nant de Thionet. 

 The upper part of this slope is masked by pine-wood and talus, and 

 outcrops of rock in situ are very scarce. The complete isolation 

 of the limestone-boss cannot therefore be proved. The general 

 characters of the cliff to the north leave no doubt in my mind that 

 it is wholly formed of schists ; all the exposures seen were of rocks 

 of this series, and these were sufficiently numerous to restrict the 

 possible connexions between the dolomite of the boss and that of 

 the cliffs below to a very narrow band. This band would run almost 

 at right angles to the strike of the schists, and thus can only have 

 been formed by deposition upon these. Its existence, therefore, 

 would strengthen the evidence in favour of the view that this 

 dolomite is an outlier from the limestones below, from which it has 

 been separated by denudation. In this case the sheet of limestone 

 of which it was once a part must have been deposited on the flanks 

 of the old schist series. 



A second line of enquiry is as to the occurrence of fragments of 

 one formation in the other. It is natural to turn to this for assist- 

 ance, for one definite case would settle the question. In the schist 

 series there are some crushed grits which must formerly have been 

 fine pebble-beds. I searched in these in vain for any fragments of 

 the dolomite. In the Trias there are bands of conglomerate, 

 crowded with included fragments. The first of those examined was 

 at the Chalets du Prejordan : a small pit there yielded numerous 

 fragments of what appeared to be altered dolomitized specimens of 

 the limestones in the central schist series. I could not, however, 

 there find any unquestionable specimens of the 4 schistes lustres ' 

 themselves. At a point near Notre Dame du Pre more satisfactory 

 evidence was obtained. The Triassic dolomites there contain some 

 beds of pebbles, many of which appear to me to be unquestionable 

 fragments of the ' schistes lustres.' Some of these included frag- 

 ments may be matched exactly in the cliff of schists, just above the 

 bank of limestone in which the fragments occur. 



A third line of argument may be based on the unaltered condition 

 of the Triassic rocks in contrast with those of the central schist series. 

 The Triassic dolomites show no sign whatever of foliation. Bertrand 

 has remarked the intensity of the puckering and folding of the rocks 

 of the centre of the massif, and admits that this is not easy of ex- 

 planation. Lory had previously recorded the occurrence of albite- 

 crystals in the limestones of the schist series, but regarded this as 

 only an illustration of the extent to which the Triassic rocks have 

 undergone alteration. If the metamorphism of the schists were 

 most strongly marked in the centre of the massif, and least so on 

 the margin, it might be explained as due to post-Triassic movements. 

 But this is not the case. The extent to which the rocks have been 

 rendered schistose depends on the character of the rocks and not on 

 their position. Some of the rocks in which the foliation is most marked 

 occur on the margin of the series within 10 yards of the dolomite. 



