732 



MISS C. A. IiAISIN ON THE 



trace westwards, so that its presence in the line of the annexed 

 section is inferential. 



Fig. 4. — Generalized Section across the Eastern Arm of the Estuary. 



IT. Summary. 



I. As to the relation of the South-Devon schists to the adjacent 

 rocks, all observations which I have been able to make support Prof. 

 Bonney's statement that the slaty beds are markedly distinct from the 

 true metamorphic rocks to the south, and that there is no evidence 

 of progressive metamorphism in this district. 



II. I have indicated some additional illustrations in these meta- 

 morphic rocks of the results following from the action of secondary 

 forces. That both the chlorite- and the mica-schists, however 

 originally formed, had been later affected by lateral pressure is shown 

 in Prof. Bonney's paper, where he several times alludes to the 

 crushing of the one series and the crumpling of the other. The 

 indications of a folding of layers in chlorite-schist are but rarely 

 exhibited with clearness ; but such structures as the transverse 

 planes locally occurring, the pitted weathering, and the " arenaceous 

 aspect " alluded to by De la Beche, seem partially due to the effects 

 of lateral pressure. In other examples there is a compressed look, 

 evidencing apparently similar force differing in direction. The 

 microscope has given additional evidence of the crushing of the 

 chlorite-rock, shown in the breaking up of quartzose layers, the 

 fracture of individual crystals, and the appearance of much secondary 

 mineralization ; while a squeezing of the beds is indicated by the 

 pressed-out form of the layers and the elongation of their constituent 

 grains. In mica- and micaceo-chloritic schists the pressure to which 

 they have been subjected has resulted in a crumpling of the layers, 

 often in the formation of strain- slip cleavage-planes exhibited in 

 hand-specimens and under the microscope, and at places has given 

 rise to slickensided, crushed and even papery schists. The larger 



