240 SELECTED NOTES FROM 



deposited. This is owing to the escape of carbonic acid, which 

 kept the lime in solution as bi-carbonate. 



Now the question is, how did the dissolved lime pass from the 

 soluble to the insoluble or ordinary form ? (I should have stated 

 that our oolitic freestones of the Cotteswolds are quite soft when 

 quarried : you may stick a pen-knife into the soft stone ; they are 

 also damp or moist, but in a few days they became very hard and 

 dry, and will turn the edge of the knife. The lime in solution has 

 passed from the soluble to the insoluble form, through the evapo- 

 ration of the water and carbonic acid.) I think the segregation 

 of diatoms may have formed the centres of attraction for the lime 

 when assuming the solid form, and, as probably the heating of the 

 water would cause the separation of the lime, the same cause would 

 ensure the solution afterwards of the siliceous particles. 



We know that these rocks have been deep in the earth's crust 

 since their original formation, and sufficiently deep to be within 

 the influence of intense heat, so that we are not likely to find the 

 diatom structure now, unless in very recent formations. 



The foregoing remarks, if near the truth, would indicate that 

 all oolitic rock structures have been produced in warm and 

 probably shallow seas. 



Paul L. Smith. 



As regards the formation of Oolitic Limestone, see Lyall's 

 Elements of Geology, 6th Edition, p. 426. 



W. H. Badbeley. 



BOTANICAL. 



Spyridia filanientosa. — In PI. 40, Figs. 2, 3, 4, will be found a 

 drawing of this pretty Alga. The form of its delicate cells has 

 somewhat tried my powers of imitation. The red alg^e, when 

 subjected to heat, turn olive-green^ thus, I think, proving the 

 colouring matter of these two great classes of marine alg^e to be 

 nearly identical. 



I think Spyridia is nearly allied to Polysiphonia ; if so, it has 

 two kinds of fruit— one, the capsule shown in drawing; the other, 

 clusters of spores on the ends of the branches. I would think 

 that the delicate fringed ends of some of the branches represent 

 these, only, if I remember aright, the two kinds of fruit are deve- 

 loped at different times of the year. I have never found the two 

 sorts on one plant. 



H. M. J. Underhill. 



