\'2'2 THE PERMIAN FORMATION. 



the Ma ian Limestone, except here and there about live feet of 



flaggy and marly beds — the Marl Slates are not found in the 

 interval, (a.) According to Sedgwick, however, they appear in the 

 lower part of the terrace which extends from Kippax towards Aber- 

 ford, east of Leeds, also north of Seacroft, in the quarries at Lindrick, 

 near Ripon, and between Knaresborough and Ripon.* In the sand- 

 pits at Glass Houghton, near Pontefract, there may be seen inter- 

 vening 1 >et ween the Lower Magnesian Limestone and the Quicksand, 

 some fourteen or fifteen feet of thinly laminated and concretionary 

 blue argillaceous limestone and shales, containing Schizodi and plant 

 remains. Traces of these beds may also now be seen in the brickyard 

 section at Conisborough already referred to. I am not at present 

 aware of any other exposures of Marl Slates in Yorkshire, but have 

 little doubt that such exist. 



In Notts the Marl Slates consist of a variable series of thin and 

 evenly-bedded grey or bluish fine grained argillaceous sandstones, 

 occasionally ripple marked grey dolomitic (b) limestones, compact or 

 oolitic, (<) and dark earthy shales. These beds contain numerous 

 imperfect plant remains, (</) fragments of fossil wood, and thin seams 

 of lignite, the casts of one or two species of mollusca, (axini,) annelid 

 tracts, and a few fish scales. These blue rocks become yellow in 

 surface exposures, and at greater depths along joints and bedding 

 planes, (apparently owing to the conversion of ferrous carbonate into 

 ferric hydrate in the presence of the oxygen of the air and of 

 infiltrating waters.) At their base is a thin but very persistent band 

 of breccia (>.) This bed varies from a compact grey sandstone to a 

 coarsely brecciated conglomerate one to three or even eight to ten feet 

 in thickness. It contains much angular coal measure debris — sand- 

 stone, ironstone, and ochreous shale — also rounded pebbles of white 

 quartz and angular fragments of slate, chert, and limestone. In its 

 coarser form it is a remarkably handsome rock, known to miners as 

 " Plumcake " or " Mingled Rock." The Marl Slates and breccia rest with 

 a pronounced unconformity on an eroded surface of coal measures, as 

 maybe seen in the railway cuttings at Kimberley, near Nottingham. 



re appears to be some doubt as to the identity of these beds in the 

 latter locftlitu is. 



a) The Permian Beds of Yorkshire, by J. W. Lucas, F.G.S., Geol. Mag., vol. 

 i\., p. 338. 



(b) Microscopic sections of this rock show closely set oolitic grains, occupied 

 (yellowish colored) crystals of dolomite, imbedded in an earthy finely 

 granular matrix. (See Pig. Lb, Plate Lx.) 



ollowing is an analysis ol this rock: Carbonate of lime, SI'S ; 

 carbonate of ma oxide of iron, 17; clay, 5 - 8=«97 - 3. 



ah Mr. OarrutherB, who is kindly examining those fossils for me, says 

 Interesting, and disclose a Bora known on the Continent, but of 

 "huh onlj imperfect materials have been deteoted in Britain." 



"> N.i'i. Thisbrecoia belongs to the Marl Slate series. It is a mistake to 

 separate tt therefrom, under a distinct head, iis Mr. Aveline does. (Geol. Survey 

 Mrmoir on country round Nottingham, 2nd edit., 1880, p. 12.) 



