Corresjjondence—Mr. A. F. Griffith. 479 



between the Deister and Siintel, there are a series of quarries, which 

 furnish excellent information upon the sequence of the rocks. The 

 strike of the beds runs from S.E. to N.W., with a very slight dip to 

 N.N.E. The lowest beds consist of a very compact, blue limestone 

 divided into thick beds, which is converted into quicklime in many 

 limekilns. Upon this, separated by argillaceous partings, follow 

 compact, oolitic, flaggy limestones with numerous examples of Exogyra 

 virgula. Otherwise fossils are scarce ; Corbiila mosensis, Buv., is the 

 one that occurs most abundantly. These beds, which according to 

 Credner attain a thickness of about 120 metres, belong to the Upper 

 Kimmeridge. Upon them follow a thickness of about 12 metres of 

 dark, in part black, marly limestones and shaly clays, with occasional 

 intercalated thin, hard, flaggy limestones, rich in fossils, especially 



jErogyra virgula, etc These beds belong to the Lower 



Portland. Over these come the strata of the Upper Portland or the 

 Eimbeckhauser Plattenkalke, which cover the whole broad ridge of 

 the Kappenberg, with a thickness, according to H. Credner,^ of at 

 least 88 metres. They are on the whole poor in fossils ; but Oervillia 

 obtusa, etc., are more or less abundant upon particular slabs. 



" On the northern slope of the Kappenberg the Plattenkalke are 

 directly overlain by the Purbeck Marls, upon which, for example, 

 the village of Nienstedt stands ; they can also be traced along the 

 road to Egestorf as far as the point where the forest road branches 

 off towards the Collnische Feld ; their thickness here amounts to 

 about 80 metres ; above them follows the Serpulit." 



The following is the sequence in the neighbourhood of Hanover, 

 as given by Striickmann in his paper " On the Parallelism of the 

 Hanoverian and English Upper Jurassic Deposits, above referred to : 



England. Hanover. 



j" Weald Clay. Upper Wealden. 



Wealden < Hastings beds. Middle Wealdeu. 



( Purbeck beds. Purbeck (Serpulite) or Lower Wealden. 



? Miinder-Mergel as a transition between 



Portland < Purbeck and Portland. 



j Portland Stone. ) Eimbeckhauser, Plattenkalke. 



V Portland Sand. j Zone of Ammonites gic/as. 



/Upper Kimmeridge Clay. Upper Kimmeridge or Virgula Beds. 



Kl-MMERIDGE <. ^"°^^^^ Kimmeridge Clay. Middle Kimmeridge or Pteroceras Beds. 

 ^ ^ j Kimmeridge PassageBeds. L. Kimmeridge (Astartian) := Nerincea 



\ beds & Zone of Terebratula humeralis. 



August, 1881. J. M. & W. H. H. 



A COEEECTIOlSr. 

 SiK, — Will you allow me to correct a mistake I made in a letter 

 appearing in your August Number ? Mr. Day's simple method for 

 determining the outcrop on any given surface of a bed or trough 

 of known cylindrical form, by means of a shadow cast in direct 

 sunlight, is equally applicable to the inverse proposition, viz., to 

 determine the form of the trough, knowing the outcrop. 



A. F. Griffith, B.A., 

 Sandridge Vicarage, Christ's Coll., Cambridge. 



St. Albans, Aug. 27, 1881. 



1 Creduer, Ob. Jura, p. 68. 



