MIDDLE CHALK—MICROSCOPIC STRUCTURE. 
509 
of silicified Inoceramus fragments, in which the original hexagonal 
mesh has become obscured owing to the stalactitic outgrowths 
of the chalcedony. The limonitic aggregates are, as already 
remarked, in short stout rods, consisting of small brown pellets 
loosely bound together, and changed externally into yellow ochre 
in many places. Several thin flakes of silvery muscovite mica 
are also present, showing feeble tints under crossed Nicols. In 
the finer residue the remains of silicified Foraminifera are very 
numerous, two specimens of Ammodiscus incertus being still 
recognisable, while the length and pyramidal form of some of the 
silicihcations point to their having been tests of Textularice 
or Bolivincv now altered beyond recognition. A few rounded 
grains of glauconite are present, one case also of a two-chambered 
cast united by a broad connection being observed. 
“ The quartz is mostly angular and colourless, only containing 
minute gas inclusions. Tourmalines have been noted, one a 
crystal, having perfect rhombohedral terminations at one end, 
but fractured at the other ; while another* is an irregular brown 
grey fragment, showing very strong absorption. 
“ Typical Beer Stone (Mr. Jukes-Browne’s specimen).— 
The residue of this weighed ‘092 gramme and consists mainly of 
highly angular quartz, accompanied by numerous flakes of 
silvery muscovite mica, green grains (rounded chamber-casts) 
and rods of glauconite, these being comparatively rare, a little 
chalcedony, some pyrites, and abundant crystals of black, fibrous 
columnar tourmaline. 
“ The following is a more detailed account of the detrital minerals 
observed 
“ Quartz Grains. — Although, as has been stated, the residue con¬ 
sists in the main of fine angular particles, some twenty larger 
grains are also present, the largest of which, coloured slightly 
yellow, has a diameter of *88 mm. The others were colourless, or 
else coloured of the same yellow tint. The larger grains contained 
rows of gas cavities. 
“ Chalcedony.—A bluish-coloured mass, showing the familiar 
stalactitic outgrowths, is the only evidence of this mineral. 
“ Rutile is present in orange flakes, of no definite form. 
“Tourmaline is very abundant in the form of aggregated 
crystalline fibres of a blue-grey' colour, recalling the tourmalines 
in Luxullianite. The absorption is very strong, the other 
characters being as usual. 
