200 
ANNALS NEW YORK ACADEMY OF SCIENCES 
area of les Ferrieres, 1 but the great mass came to the surface near the area of 
extreme disturbance. This outburst coming at the close of Commentry’s 
history made the thrust which doubled up the Glissement beds, pushed the 
rocks beyond and increased the dip throughout the Pegauds area. Fayol, 
in his reply to Renevier’s objections, grants that this outburst affected the 
rate of clip, but only to increase it by about 25 degrees; and he maintained 
that it had nothing to do with causing the prevalent dip of about 30 degrees. 2 
Fayol’s position is right to some extent, but one must allot to the diori- 
tine outburst a much greater and wider influence than he admits. The 
dikes are present even in the area of les Ferrieres, so that there is reason to 
believe that the mass extends under the coal measures of the entire basin, 
or at least that it extends across the northerly portion, thus causing a serious 
dislocation in that whole region. 
Yet, even with that extension, there remains a serious dip to account for. 
Renevier’s suggestion 3 that the synclinal structure observed in an east and 
west direction is due to gradual subsidence through carbonization and com¬ 
pression of the soft materials, is in accord with conditions described in 
Pennsylvania, Iowa and other states. The gradual change in mass cer¬ 
tainly accounts for the synclinal structure and for a dip of five degrees; the 
intrusion of a sheet of dioritine accounts for the crushing and polishing as 
well as for much of the clip in the western part of the areas; but these do 
not account for all of the features. 
Secular movements in the basin. 
This leads to the last matter to be considered in this paper, which already 
has exceeded the limit intended at the outset. 
The form of delta-hypothesis under consideration insists upon great 
depth of the basin as a pre-requisite. The writer is far from saying that it 
should be rejected on the ground of inherent improbability, for such a 
depression in the surface is not in any sense impossible. But if a hypothesis 
can be presented which is more in accord with what are known to be the 
normal conditions in nature and which, at the same time, meets equally well 
the requirements within this area, it is preferable. 
The region of which the Commentry basin forms a small part had been 
undergoing prolonged and serious disturbance. De Launay’s admirable 
synopsis makes this clear. A great fault marks the westerly side of the 
syncline for much of its length; though that is not recognizable on the west 
1 Fayol: Commentry, pp. 44-47. 
2 Reunion etc., p. 68. 
3 Reunion etc., pp. 67, 68. 
