A. Atrypa-flexuosa Zone, Skelgill.
This consists in part offinely-divided micaceous material,with chlorite of the usualtype, and some quartz, but thereis also a considerable amountof carbonate, and the rock effervescesfreely with cold diluteacid. It differs therefore notably fromthe others, and maybe described as an impure limestone [20,008].
B. Green Streak,Argenteus Zone, Skelgill (with parts of adjoininggraptoliticmud-bands).
This specimen shows very pronounced colour-banding.The palegreenish-grey ‘streak’ is strongly differentiatedfrom the other part, which is dark-grey. On ignition for 30minutes, the ‘green streak’ becomes somewhat paler,nearly white; and the dark bands are reddened.
Under the microscopethe ‘green streak’ is seento be closely similarto the Browgill Shale (G, p. 132), thoughof somewhat finertexture, and with much more pronounced orientationof the flakesof mica and chlorite. Grains of quartz determinableunder ahalf-inch objective are quite rare.
The dark rock enclosingthe streak, which belongs to the graptoliticbands, appearsto be essentially of the same composition, althoughthe structureis partly obscured by the presence of a largeamount of darkbrownish-black material. Since this reddens onignition, itis probably in part ferrous sulphide and in partcarbon [20,006].
C. Green Streak, Pont Erwyd
This is quite similar in compositionand general character tothe ‘green streak’ fromSkelgill, but slightly coarserin texture: very angular fragmentsof quartz are easily visibleincertain bands.
The Rock
...
This 250-word extract was created in the absence of an abstract.
