Notices of Memoirs — Dr. D. Woohicott — The Permian. 513 



internal reflections; hence rays cannot emerge freely at right angles 

 to the plate. 



Further, if a plate of brown phlogopite be rotated in its own 

 plane when in an oblique position, it exhibits axis-pleochroism, 

 the axial colours being the same as those observed when the plate is 

 examined with a nicols prism or a dichroscope. The varieties which 

 show this axis-pleochroism in ordinary light to best advantage are the 

 rich brown phlogopites, which show the pronounced axial tints on 

 the base. 



A plate of coloured muscovite or ordinary biotite, if examined in 

 the manner liere described, shows no pleochroism. 



A basal cleavage plate of brown phlogopite therefore provides an 

 instance of a mineral which exhibits axis-pleochroism when examined 

 in ordinary light, without the use of a polarizer or a dichroscope. 



nsroTioES oif ]vi:e]veoii?.s. 



I. — PRELIMINARY JS'OTE ON THE CLASSIFICATION OF THE PeKMIAN OF 



THE Nokth-East OF ENGLAND.^ By David Woolacott, D.Sc, F.G.S. 



SEDGWICK, Howse, and King classified the Permian according 

 to the nature of its stratification or of the structures occurring 

 in it ; but as the bedding of the different divisions is often alike, 

 and as the structures — whether concretionary, brecciated, pseudo- 

 brecciated, or cellular — are not confined to particular horizons, 

 divisions named on this basis are misleading and unsatisfactory. The 

 use of the term * fossiliferous ' to mark off a division is also in- 

 admissible. In the following classification the limestone is typically 

 developed at the place the name of which is used to designate a group 

 of strata. The divisions in descending order are — 



Middlcslrough Red Beds with Salt. — Red marls, marly sandstones 

 and lenticular beds of salt, anhydrite, and gypsum with foetid fossili- 

 ferous magnesian limestones. 300 feet. 



HoJcer Limesto7ie. — Yellow limestone, regularly bedded ; some beds 

 compact, others formed of minute hollow spheres. 100 feet. 



Fulwell Rocks. — Bedded yellowish and brownish concretionary (of 

 various types) and non-concretionary limestones, in places highly 

 fractured and brecciated ; cemented crush breccia occurs locally. 

 Base often much disturbed by beds from below being forced into it, 

 and by falling of lower layers into fissures and gashes. Irregular beds 

 of amorphous marl are associated with these beds. Two fossiliferous 

 horizons occur : one of fish remains at Fulwell, and the other of 

 invertebrata at Byers Quarrj'. 150 to 200 feet. 



Ilarsden Rocks. — Bedded yellow and brown limestones, slightly con- 

 cretionary in places. Irregular masses of white limestone resembling 

 Mountain Limestone occur. Brecciated beds (cemented crush breccias) 

 occur at different horizons. In places highly folded and fractured, 

 but sometimes little disturbed. Breccia-fissures and breccia-gashes 



' Abstract of Paper read at British Association Meetiug-, Winnipeg, in Section (C) 

 Geology, August, 1909. 



DECADE V. — VOL. VI. — NO. XI. 33 



