56 Dr. A. Hubert Cox — South Staffordshire Fire-clays. 



EXPLANATION OF PLATE V. 



Fig. Eocystis prim^va. 



1. The liolotype, reproduced from Dawson's fig. 220. 



2-6. Diagrams illustrating the direction and strength of the folds in five 

 plates, viz. (2) E 7611, (3) E 7604, both being imprints of the inner 

 face ; (4) G. F. M. /, (5) G. F. M. e, (6) E 7603, these being imprints of 

 the outer face. In (2) to (5) there are ten folds to each plate ; in all 

 there can be distinguished three main folds Xi and two folds nearly as 

 strong running east and west ; subsidiary folds occur in the spaces 

 between all of these, except the space in the E.S.E. sector (as seen 

 in the external imprint), and are rare in the corresponding W.S.W. 

 sector. 



7. E 7602, showing a plate and a columnal ; (a) externa,!, (&) internal 



imprint, x 4 diam. 



8. G. F. M. c. An imprint of a plate sujiposed to show marginal pores, as 



received, x 8 diam. 



9. The same imprint after removal of more matrix. x 8 diam. 



10. E 7602. {a) External imprint of a plate ; (6) columnal. x 8 diam. 



11. G. F. M. a. Internal imprint of a stellate plate of normal form, x 4 diam. 



12. G. F. M. b. External imprint of a plate. X 4 diam. 



13. G. F. M. d. Imprint of columnal (?). x 8 diam. 



14. G. F. M. g. Squeeze from imprint of a columnal. x 4 diam. 



15. Suggested reconstruction of a columnal in solid section, x 4 diam. 



16. G. F. M. h' . Wax squeeze of an undetermined plate, (a) from above, 



(h) from the side. x 4 diam. 



17. G. F. M. I. Wax squeeze of an external imprint, possibly the infilling of 



a columnal. x 4 diam. 



18. G. F. M. j. Wax squeeze of an external imprint of an undetermined 



plate. X 4 diam. 



19. G.F. M. fc. Ditto. 



20. G. F. M. h. Ditto. 



Drawings by G. C. Chubb, from the specimens and from pencil drawings by 

 the author. 



II. — Notes <m some South Staffohdshire Fike-clays aud THKiR 



Behaviour on Ignition. 



By Arthur Hubert Cox, M.Sc, Ph.D., F.G.S. 



ALL geologists are familiar with those changes effected iu 

 argillaceous rocks under the influence of heat from igneous 

 intrusions, changes that result in the formation of such rocks as 

 ehiastolite-slate, andalusite-hornfels, etc. It is therefore somewhat 

 surprising that the changes produced during the artificial heating of 

 clays should remain comparatively unknown to the body of geologists, 

 although such changes are produced every day on a large scale 

 during the baking of clays for the manufacture of pottery of various 

 kinds. These changes liave, indeed, been very little studied from 

 the mineralogical standpoint. It might at first sight be expected 

 that anj- changes brought about artificially by the action of heat on 

 a clay would compare somewhat closely with those resulting in an 

 argillaceous rock when subjected to contact-metamorpliism — at any 

 rate in the normal case of the latter change — when there is no 

 transference of material from the igneous to the sedimentarj' rock. 

 Yet such is hardly the case ; there are certainly points of resem- 

 blance, but there are also very notable differences. It must be made 

 clear that the clays used in the experiments to be described were 



