OOLITK OF Tin: COTTKSWOM) HILLS. 563 



grouiulraass or pasto .... and throughout this paste immense 

 numbers of rutile crystals are seen." This corresponds with the 

 granular substance I have referred to as the chief constituent in the 

 residue of the Oolite ^farl. 



Specimen No. 2 was collected from about the centre of the marl 

 and contains 3-1 percent, of residue. Like the last-mentioned, this 

 consists chiefly of the granular silicate of alumina, and associated 

 with it arc small Hakes of mica, quartz-grains, and a considerable 

 quantity of very minute crystals of zircon. The quartz-grains 

 averaged 0"0S mm. in longest diameter. 



No. 3. This specimen was taken from the top of the marl. It 

 yielded »3'5 per cent, of residue, chielly flakes of mica, decomposed 

 felspar, and (piartz-grains, the latter averaging about O'l mm. in 

 greatest diameter. 



The Upper Freestone. — Two specimens were collected from the 

 Upper Freestone at Leckhampton, where it is about 30 feet thick. 



No. 1 yields 0-9 per cent, of residue, chiefly quartz-grains and 

 pyrites, the latter sometimes in the form of minute spheres. 



No. 2 yields 0*0 per cent., consisting of quartz-grains and 

 mica. 



A residue from these freestones at Cleave contains quartz with 

 felspar and a few crystals of zircon. The proportion of felspar was 

 the chief feature of interest. 



Specimens were also collected from the Upper Freestone exposed 

 in Chedworth Wood, to which reference has been made in Part I. 

 of this paper. It will be remembered that there were two varieties, 

 the normal yellow and the blue. A specimen of the former yielded 

 0*8 per cent, of residue, consisting of quartz, a quantity of felspar, 

 and some amorphous silica, chiefly in the form of casts of GlrvaneXla 

 tubules. 



Of the blue variety two estimations of the residue gave 7'5 and 

 1*7 per cent, respectively. There is a considerable discrepancy be- 

 tween the two, and also between these and 0*8 per cent, obtained 

 from the yellow oolite. This entirely arises from the varying pro- 

 portion of pyrites in the respective residues. This sulphide of iron 

 is more plentiful in the blue oolite, and where it occurs in consider- 

 able quantity, as in the case of the specimen which yielded 7 '5 per 

 cent, of residue, the rock soon crumbles on exposure to the atmo- 

 sphere — this, no doubt, owing to the oxidation of the pyrites. The 

 sul[)hide of iron occurs chiefly in a spherical form, and there are 

 either casts or replacements of the tests of foraminifera and other 

 organisms. 



The Argillaceous Bed., ivhich terminates the Upper Freestone at 

 Chedworth. — This bed yielded 67'9 per cent, of residue, consisting 

 of quartz, some felspar, mostly decomposed, and mica. I3ut the 

 chief constituent of the residue is silicate of alumina, and it corre- 

 sponds in every respect with that found in the Oolite Marl. In the 

 bed at Chedworth this silicate of alumina occurs in such quantity 

 that it was easy to obtain sufficient for chemical analysis, and, with 

 the object of proving beyond doubt that it is a silicate of alumina, 



Q. J. G. S. No. ^^?^. ' 2r 



