Q. W. Card—FlexiUUhj of Rocks. 119 



calcite ; mostly of about three or four millimetres diameter. These 

 appear of a brown colour when very small, but when larger this 

 appearance is seen to be due to a coating of ferruginous matter 

 which lines the cavity in which the crystals occur. In one case a 

 perfect geode of about 1 cm. in diameter and lined first with 

 a ferruginous coating and then with calcite crystals occurred. The 

 position of such a nest would be indicated externally only by a 

 slight elevation on the surfaces of the lamina. This was especially 

 the case with the geode mentioned above ; its position was clearly 

 indicated by a slight bulging of either side of the lamina in which 

 it occurred, the protuberance being flattened and marked with con- 

 centric rings. It would seem as if such a geode might mark 

 an incipient stage in the formation of some of the concretionary 

 structures of which this series affords so many beautiful examples. 

 A specimen in my own collection may well have originated in this 

 way ; it is flattened on one side, irregularly dome-shaped on the 

 other, with a cavity open on the flat side, and extending into 

 the interior of the dome. There are no cracks or any other com- 

 munication across the planes of bedding, and the nests occur quite 

 isolated — not in strings. It is therefore evident that they have 

 originated in the bed itself.^ These structures will again be referred 

 to when the case of the flexibility is dealt with. 



An analysis made under the superintendence of my friend Mr. "W". 

 Tate, A.E.C.S., gave the following results : — 



CO2 46-476 



CaO 30-744 



MgO 21-169 



FeO -518 



SiO, 1-028 



Total 99-935 



Notwithstanding the friability of the stone, sections can readily 

 be prepared transverse to the bedding planes. Mr. F. Chapman, 

 who prepared mine, tells me he had no difficulty after soaking the 

 specimens in Canada-basalm. A low magnifying power reveals a 

 large number of irregularly-shaped empty spaces, in the main 

 arranged linearly in directions parallel to the bedding, but also 

 occurring promiscuously through the section.^ With a ^-inch 

 objective the section is resolved into an aggregate of grains of 

 feebly-polarizing dolomite, the larger grains averaging about 

 •01 mm. in diameter, with a very few minute grains of quartz, 

 and here and there of blue- and of brown-coloured minerals. With 

 a ^-inch, and still better with an -l-inch, the grains are seen to be 

 irregular in outline ; the larger grains (sometimes attaining a 

 diameter of -02 mm.) frequently appear to be intergrown in such a 

 way that a convexity of one fits into a convexity of another, or a pro- 

 jection into a depression. Very rarely a minute piece of mica occurs. 

 Having described the general appearance of the stone, the nature 

 of its flexibility remains to be dealt with. In every case I find 



^ Sedgwick, op. cit. 



3 See Woodcut, Fig. A., p. 123, infra. 



