STEVENSON, COAL BASIN OF COMMENTRY 
201 
side of Commentry, yet there, as well as for some distance eastwardly along 
the southern border, the coal measures abut against the granite. It would 
seem wholly in accord with the observed phenomena to suppose that the 
unstable conditions continued and that there was a differential sinking of 
the bottom of the basin, increasing toward the southwest and south; not a 
constant but an intermittent subsidence, as is known to be the condition in 
faulted regions. During a long period of very gentle subsidence, the Grande 
Couehe and the immediately overlying beds accumulated; an abrupt adjust¬ 
ment after the period of comparative cpiiet would bring about serious changes 
in the watercourses of the little area, during which the black shales of the 
Gres Noirs could be formed by destruction of exposed portions of the Grande 
Couehe. Even the distortion of the Grande Couehe in the Longeroux 
trench might be due to a disturbance of this type. 
A differential subsidence combined with the effect of compression and 
carbonization would account for the high dips which have been regarded as 
original. The distribution of the coarse materials as well as the absence of 
horizontal beds alike favor the supposition that the water was shallow and 
that the great apparent depth is due to subsidence. This hypothesis is 
merely the outgrowth of de Launay’s presentation of the character of move¬ 
ments throughout the region under consideration. He asserts, rightly enough, 
that there is nothing incompatible with the delta theory in the supposition 
that movements such as he describes had taken place during the formation 
of the coal and had given to the lake, step by step, the great depth which is 
found to-dav . 1 
Appendix. 
Jukes on formation of coal beds. 
One cannot fail to recognize the typical features of delta deposit every¬ 
where in the excavations at Commentry and students should be grateful to 
the engineer who chose this mode of mining, for there the conditions, which 
elsewhere have been only surmised, are exposed in full day. Study of these 
phenomena led Fayol to formulate his doctrine, which, he says, is not abso¬ 
lutely new; it was entertained by the first savants who studied coal, but 
afterwards hypotheses as improbable as insufficient were presented. He is 
confident that these will be rejected when men discover that simultaneous 
transport of vegetable and mineral materials can give distinct beds and 
when they have seen that* the delta theory explains all of the coal measure 
phenomena . 2 
1 Reunion etc., pp. 101, 102. 
2 Commentry, pp. 19, 20. 
