Prof. T. G. Bonney—On the Ightham Stone. 299 
one being rather less than a foot in thickness, the other perhaps 
about six inches,! and well-defined bands of ironstone extended for 
a foot or so below them. Beneath them consolidated sand was rare 
or absent. The relation of these masses to the surrounding sand 
left no doubt in my mind that they were of concretionary origin ; 
the sand being cemented by deposition of secondary silica. 
When examined with the microscope the green rock is found 
to consist almost entirely of grains of quartz, often about :02” or 
025” diameter, which for the most part are remarkably well rounded. 
These contain, in variable number, cavities, generally very small 
and commonly empty, and occasional microlithic enclosures, such as 
hair-like belonites, brownish-olive films(mica or in some cases tourma- 
line ?), and occasionally zircon. One grain also contains a number 
of yellowish-brown needles about 005” long. The general aspect 
of these grains leads me to conclude that they have been derived 
from a granitoid rock. With them occur a few grains of a chert 
(perhaps not generally so well rounded) varying in colour from 
brown to colourless, and sometimes apparently containing fragments 
of organisms. Rounded grains of limonite also occur as is common 
in the Folkestone Sand. There are also a few fragments distinctly — 
of organic origin, presently to be described. The cementing material 
is chalcedonic quartz, the tiny crystals commonly growing outwards 
from each sand-grain, like a fringe, having a moderately distinct 
radial arrangement. The surfaces of adjacent grains are rarely quite 
in contact, but even at the nearest parts are separated by a thin 
Felix Oswald dol. 
Ightham Stone x 35. 
film of microcrystalline silica. Now and then an interspace between 
the fringes is occupied by chalcedonic silica, confusedly arranged, or 
more rarely by limonite, which probably is associated with silica. 
Occasionally brown films may be noticed in the quartz grains them- 
selves, as though the limonite had made its way into cracks. The 
? From their position in the scarped face of the sand, they could not be reached for 
measurement without an amount of trouble that would have been wasted. 
