o()2 MB. E. WETHERED ON THE INFEIUOR 



Specimens of the Lower Freestone proper were collected at Leck- 

 hampton Hill, near Cheltenham. 



No. 1, from near the base of the series, yielded 0*8 per cent, of 

 ijuartz-grains, the grains as large as 0*16 mm. in their longest 

 diameter, and averaging 0"13 mm. One or two fragments of felspar 

 and some zircon were noticed. 



No. 2 yielded 0*9 per cent, of residue, consisting almost entirely 

 of quartz. 



No. 3 gave 1-1 per cent, of quartz, with some little felspar and 

 mica. 



No. 4. The residue contains little else than quartz-grains, which 

 average about O'll mm. in diameter. 



TJie Oolite Marl. — The Oolite Marl is a well-marked boundary 

 between the Lower and Upper Freestones in the Northern Cottes- 

 wolds. It attains its greatest development at Cleeve and Leck- 

 hampton Hills, near Cheltenham, where it appears as a yellow, 

 calcareous, argillaceous deposit, about 7 feet thick. Specimens for 

 examination were collected from Leckhampton Hill, and were taken 

 from the bottom, middle, and top of the marl. 



No. 1, from the base, contains 3*2 per cent, of residue, which, 

 in the acid solution, is mostly a flocculent substance. When mounted 

 on a slide and placed under a microscope, the most conspicuous con- 

 stituents in the residue are scales suggestive of sericite, and for 

 some time I so regarded them. This, however, was an error, arising 

 out of the way in which I prepared the specimens for mounting. 

 My method is, after washing free from calcium chloride, &c., to dry 

 the residue on a watch-glass ; but, not being satisfied about the 

 supposed sericite, I removed a portion of the residue from the filter, 

 and while moist spread it over a glass slide. In this the thin scales 

 disappear, and the residue consists of an extremely fine granular 

 substance, with very small flakes of mica and other doubtful mineral 

 fragments. It was further discovered, when I dried the residue on 

 a watch-glass, that the granular substance coagulated and enclosed 

 some of the fine detrital material with it, especially the mica. 

 This, then, was the origin of the supposed scales of sericite. The 

 granular substance was afterwards proved to be chiefly silicate of 

 alumina. 



There is also another matter of interest connected with this 

 silicate of alumina, to which Mr. Teall kindly called my attention. 

 Examined under a high-power object-glass there is found to be 

 associated with it a quantity of extremely minute crystals of rutile, 

 corresponding exactly with those figured by liosenbusch *, and to 

 which Zirkel first called attention in clay-slates and roofing-slates ; 

 hence they have been termed "clay-slate needles" {Thonschiefer- 

 nadehi). 



Mr. W. M. Hutchings t has also shown that some Carboniferous 

 argillaceous beds at Seat on contain what he terms " a sort of 



* ' Microscop. Physiogr. of Rockrnaking Minerals,' transl. Iddings (1888), 

 pi. \v. fier. 4. 

 t Geol. Mag. (1890) p. 271. 



