852 



PERMIAN COMPACT LIMESTONES. 



[Ch. XXIIL 



studying the phenomenon in the Marstou Rocks, 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 



Fig. 447. 



a. Fenesiella reti/ormis, Sclilot. sp. 



Syn. GorgoniainfandihuUformis, Goldf. : Reteporaflustracea^ Phillips. 



h. Part of the same highly magnified. 



Magnesiaii limestone, Humhleton Hill, near Sunderland.* 



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

 ing 8 inches in width. The same zooph3^te, or rather mollusk, with several 

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

 Shells of the genera Producius (fig. 448) and Sti^oj^halosia (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. 



Producius horridus, Sowerby 

 (including P. calvus, Sow.) 

 Junderland and Durham, in Magnesian 

 Limestone ; Zechstein and Kupfer- 

 schicfer, Germany. 



Spirifer undtdaiu.% Sow. Min. Con. 

 Syn. Triogonotreta undulata, King 

 Monogr. 

 Magnesian Limestone. 



yellow magnesian limestone. They are accompanied by certain species of 

 Sinrifer (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 

 Terehratula^ 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 compact 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, pL 2. 



