Dale — Drag-Folding in Alabama Marble. 321 



intensely plicated between the bedding planes but that 

 this plication must have taken place both in the strike and 

 the dip directions, and had resulted in the formation of 

 marble lenses coated with a film of schist. Fig. 1 shows 

 sections of such lenses on the strike face of a block and 

 ^g. 2 on the dip face. The latter shows intricate plica- 

 tions of the schist laminse on both sides of the lenses 

 which led up to the formation of the lenses. 



In order to ascertain whether the micro-texture of the 

 marble near these lenses showed anything abnormal, thin 

 sections were made of pieces from two blocks, one section 

 in the dip direction, the other in the strike direction. Only 

 that in the dip direction from the block represented in 

 fig. 1 showed grain elongation in the direction of the dip. 

 This corroborates evidence from a thin section of the 

 marble at Gantts quarry showing that during metamor- 

 phism there was a powerful pressure along the strike, i. e. 

 about N. 10° E. which is implied in the occurrence of the 

 lenses. 



Conclusion: The formation of these schist-coated 

 marble lenses involves not only extreme intra-bedding 

 plication (drag-folding) but this must have occurred in 

 rectangular and concentric directions in order to trans- 

 mute plications with longitudinal axes into lenses. 



Of course the schist laminse are minute layers of clay 

 particles of inorganic sedimentary origin metamorphosed 

 into more or less fibrous muscovite, etc. 



Sheffield, Mass., Oct. 13, 1921. 



