19I3-] STEVENSON— FORMATION OF COAL BEDS. 117 



stems and branches of trees. The '* horse," about which Buddle^^^ 

 wrote many years ago, belongs in this category. This " washout," 

 170 to 340 yards- wide, had been traced for about 2 miles in Colford 

 High Delf seam. The material is sandstone, through which a tunnel 

 had been driven where the width is about 200 yards. Under this 

 " horse," the coal is 4 inches to 7 feet thick and usually it is injured 

 by sand patches from the roof ; but it contains no gravel, bowlders or 

 fragments, though the last occur in the sandstone. Some portions of 

 the " horse " consist of sandstone breccia, with pebbles of quartz, 

 like those of the Forest pudding stone — which underlies the Car- 

 boniferous limestone — with fragments of coal, ironstone and plant 

 remains. The underclay is wholly regular. 



It is unnecessary to cite additional instances. The phenomena 

 are familiar in British, French and German coal fields. They have 

 been observed in the Laramie area of Colorado and New Mexico, 

 and they are characteristic of the vast peat area of the Rhine low- 

 lands, where they have been described by Lorie. All are alike,, 

 whatever the age may be ; they are the work of sub-aerial streams,, 

 some of which existed while accumulation of the vegetable material 

 was in progress, while others began existence at a later date. 



Flexed Strata. 



The presence of flexed shales or coals between beds of undis- 

 turbed rocks has been regarded as evidence of slips or slides of soft 

 material on submerged slopes ; but they cannot be accepted as evi- 

 dence of such conditions until, first of all, the existence of the sup- 

 posed conditions has been proved in other ways : for this structure is 

 so familiar as to be almost normal in all strongly disturbed areas — in 

 the Appalachian basin, in the Nord basin or in the little basin of 

 Commentry. To bring about the condition there must be a soft, 

 yielding material between beds of more resistant rock. Lohest^-** 

 has shown that movements occur in the coal without disturbance of 



"'J. Buddie, "On the Great Fault called the "Horse" in the Forest of 

 Dean Coal Field," Trans. Geol. Soc. Land., II., Vol. VI., 1842, pp. 215, 218. 



^ M. Lohest, " Sur le mouvement d'une couche de houille entre son toit 

 et son mur," Ann. Soc. GcoI. de Bclgique, Vol. XVII., 1890, Mem., p. 125. 



