352 



PERMIAN COMPACT LIMESTONES. 



[Ch. XXIII. 



studying the phenomenon in the Marston Books, on the coast of Durham, 

 I found it impossible to form any positive opinion on the subject. The 

 well-known brecciated limestones of the Pyrenees appeared to me to 

 present the nearest analogy, but on a much smaller scale. 



The fossiliferous limestone (No. 3) is regarded by Mr. King as a deep- 

 water formation, from the numerous delicate bryozoa which it includes. 

 One of these, Fenestella retiformis (fig. 44*7), is a very variable species, and 



Tig. 447. 



a. Fenestella retiformis, Schlot. sp. 



Syn. Gorgonia infundibuliformis, Goldf. : Reteporajlustracea, Phillips. 



b. Part of the same highly magnified. 

 Magnesian limestone, Humbleton Hill, near Sunderland.* 



has received many different names. It sometimes attains a large size, measur- 

 ing 8 inches in width. The same zoophyte, or rather mollusk, with several 

 other British species, is also found abundantly in the Permian of Germany. 

 Shells of the genera Prodnctus (fig. 448) and Strophalosia (the latter 

 an allied form with teeth in the hinge), which do not occur in strata newer 

 than the Permian, are abundant in this division of the series in the ordinary 



Fig. 448. Fig. 449. 



Productus horridm, Sowerby 

 (including P. calvus, Sow.) 

 Sunderland and Durham, in Magnesian 

 Limestone; Zechstein and Kupfer- 

 schiefer, Germany. 



Spirifer wndulatus, Sow. Min. Con. 

 Syn. THogonotreta imdulata, King's 

 Monogr. 

 Magnesian Limestone. 



vellow maguesian limestone. They are accompanied by certain species of 

 Spirifer (fig. 449), and other brachiopoda of the true primary or paleozoic 

 type. Some of this same tribe of shells, such as Athyris Roissyi, allied to 

 Terebratula, are specifically the same as fossils of the carboniferous rocks. 

 Avicula, Area, and Schizodus (see above, figs. 444, 445, 446), and other 

 lamellibranchiate bivalves, are abundant, but spiral univalves are very rare. 

 The comp>act limestone (No. 4) also contains organic remains, especially 

 bryozoa, and is intimately connected with the preceding. Beneath it 

 lies the marl-slate (No. 5), which consists of hard, calcareous shales, 

 marl-slate, and thin-bedded limestones. At East Thickley, in Durham, 

 where it is thirty feet thick, this slate has yielded many fine specimens 

 * King's Monograph, pi. 2. 



