Reddish brown rock. Medium sand grade.
Round to sub-round grains of quartz, often with a thin rim of red hematite. Mainly reddish and pink-brown grains, fewer white grains and very few black grains. Well sorted and well cemented.
No fizzing with acid, so does not contain significant carbonate. 

Laminations can be observed in sample L326b. There is an inter-layering of coarser and finer laminae.

Fine laminations can be seen when the thin-section is held up to the light. 
Moderately well rounded quartz grains with thin rims of hematite, and overgrowths of quartz in optical continuity with the original grain. 
Occasional grains of very fine quartzite, microcline, plagioclase, mica and decomposed fine-grained igneous rocks. 
Siliceous cement and the secondary quartz overgrowths hold this rock together.

The grains are finer as a whole in L326b, and less well rounded.

Probably deposited in an aeolian environment, since it almost entirely comprises well sorted and well rounded quartz grains.

ferruginous sandstone
ferruginous arenite

Mainly medium sand (to coarse sand in the case of L327a). 
Yellow-brown iron stained quartz, cemented by the same yellow brown oxide. A few larger quartz grains up to 5 mm long. Grains are angular to sub-rounded, and poorly sorted. 
Fizzing with acid, indicating that there is a carbonate cement.

Angular to sub-angular grains of quartz, displaying undulose extinction. 
Most have thin brown rims of iron oxide. 
A few grains of feldspar. 
Minor carbonate cement (sparite).

Deposited in an aqueous environment, since it is not clean enough to be aeolian.

Iron staining 
Hematite (Fe₂O₃) → red (blood-red, cherry-red, brown-red) iron-staining 
Limonite (FeO(OH)•nH₂O) → yellow or brown iron-staining

The yellow colour of this rock is probably produced by limonite.

ferruginous sandstone

Dark grey rock, mainly fine sand.
Does not react with acid, probably mainly quartz. 
Some glints of mica. 
Cement reacts with acid, so it is at least partially carbonate. 
Band of brown-grey material is due to weathering.

The thin-sections are only cut from dark grey, unweathered region of the rock. They are best viewed under high magnification.

Sub-angular to sub-rounded quartz grains. Mainly fine sand, with a significant proportion of silt. >15% clay, so this is a wacke.
A few white mica flakes and opaque grains.
The main cement is carbonate, though the grains are also partially cemented by the clay grade grains.

Wackes are commonly produced by turbidity currents, though we cannot be sure without seeing graded bedding.

sandstone
wacke

Pale buff coloured, crystalline rock. 
Numerous cavities, thought to have been formed by shrinkage during alteration of primary calcite (CaCO₃) to secondary dolomite (CaMg[CO₃]₂). There is a weak reaction to dilute acid, which suggests that there may be some calcite remaining. 
Colourless crystalline material infilling holes.

Almost entirely made up of very fine grains of dolomite (which tends to show more rhomb shaped crystals than calcite).
Irregular cavities into which well-developed rhomb crystals of dolomite have grown. Note that one should distinguish between the cavities in the rock (with rhombs of dolomite) and those due to the preparation of the sections.

It is thought that this rock was initially made-up of calcite. The alteration from calcite to dolomite, with its consequent increase in specific gravity and decrease in volume, accounts for the formation of the cavities.

dolmitic limestone
dolomite
magnesian limestone

Grey-buff colour rock made up of ooids, mainly medium grained and spherical. 
Some shell and lithic fragments. 
Well compacted and cemented by calcite, which fizzes with acid.

The ooids look brown. They are made up of calcite grains much smaller than the thickness of the slide (which is 30μm). These small grains refract, diffract and reflect light travelling through the slide producing the brown appearance of the ooids. Most of the ooids were formed around a central nucleus (usually an angular quartz grain, sometimes a shell fragment).The calcite forming the ooids is mostly too fine-grained to distinguish individual crystals. 
Only some of the ooids appear to be touching in thin-section, but taking account of their 3D relationships, the rock is probably clast supported.
Rounded shell fragments including aragonite bivalve moulds and silicified brachiopods. 
Occasional quartz grains.
Clean, colourless calcite cement.

This is a packstone (Dunham naming system) or oo-biosparite (Folk naming system).

Deposited in a moderate energy, marine environment.

oolitic limestone
packstone
oo-biosparite
oolite