Sollas — Supplementary Remarks on Oldhamia. 359 



9. In some cases a definite black line marks the surface of the 

 undulations of a single lamina. This is produced by some ferru- 

 ginous material soluble in hydrochloric acid. It is suggestive of 

 the previous existence of an organism, the decay of which might 

 have led to a deposition of some compound of iron. Further obser- 

 vation of cleaved specimens shows, however, that the ferruginous 

 layer is not restricted to the Oldhamia markings, but occurs evenly 

 over the surface of the lamina?. 



10. More frequently the cleavage laminae are coated with 

 chlorite, which appears in some cases of greater thickness within 

 the grooves which represent in imtaglio the ridges of Oldhamia. 



11. In some specimens, straight or undulating, black lines 

 run along the axis of a series of folds : these are produced partly 

 by a change in direction of black rods, which in other cases run 

 parallel to the cleavage laminae, and partly by the in-filling of 

 minute cracks formed along the axis of the folds. 



12. In such cases the folds are usually sharper and closer 

 together. Seven successive folds were counted in a distance of 

 0*8 mm. in one instance. The sericite scales are sharply bent in 

 parallelism with the axis. In a hand specimen these sharp, sheared, 

 or faulted folds produce an appearance of false bedding on a small 

 scale. 



13. They appear to represent a further stage in the folding of 

 the rock, which commences with the broader wrinkles of the usual 

 kind. 



14. These appearances are remarkably similar to those of 

 " ausweichungsclivage," described by Heim in his " Gribergsbil- 

 dung." 



15. They also suggest a resemblance to the modified bedding 

 foliation and cleavage foliation described by Prof. Bonney in his 

 last Presidential Address to the Geological Society of London 

 (figs. 3 & 4, p. 70), but differ in the fact that the sericite scales 

 are conformable with the foldings in the Oldhamia phyllades, but 

 not in the quartz gneiss of Muchalls, where they lie at right angles 

 to the chord of the folds. 



16. "While these observations tend to show that Oldhamia is but 

 the incipient stage of " ausweichungsclivage," they throw no light 

 on the remarkable radiate form of the markings. 



