THE CRETACEOUS SYSTEM 505 



quantity of intermingled argillaceous matter. Thus at Heacham 

 and Hunstanton the stage has the following composition : 18 



I'V,.',. 



Zone of (f>. Hard whitish chalk in rather thin beds ... 35 



Offaster -(4. Rough dark-grey chalk with a layer of green-coated 



sphcericus [ nodules at the base (Totternhoe stone) . . 2 



,. f (3. Hard creamy white chalk . . . . .18 



| 2. Hard grey rough and shelly chalk with a layer 



c/iucn. -t of g reen . coate( j nodules at the base ... 4 



U- Hard white nodular limestone 1J 



66J 



The hard shelly chalk (No. 2) is often called the " Inoceranms 

 Bed " because it is crowded with fragments of Inoceramns shells, 

 probably of Inoc. latus. It also contains Holaster subylobosus and 

 Acanth. rotomagensis ; but the former here ranges throughout the 

 stage, so that it is convenient to take another urchin as index for 

 the upper zone, and for this purpose Offaster sphcericus, common in 

 the upper beds of Lincolnshire and Yorkshire, seems best. 



In Lincolnshire the only noticeable variations are (1) the red and 

 pink coloration of two beds in the zone of Offaster sphcericus near 

 Louth ; (2) the reappearance of the Belemnite marl, which is absent 

 near Hunstanton, but is often 2 feet thick in Lincolnshire, and is 

 sometimes stained dark red or purple. The Totternhoe stone is a 

 constant bed about 2 feet thick throughout the county. 19 



In Yorkshire the Lower Chalk maintains the Lincolnshire facies 

 along the greater part of the escarpment, but at Speeton it shows some 

 changes. The zone of Sch. varians expands to 77 feet, and the 

 lower part consists of nodular chalk in alternating pink and white 

 bands. The zone of Offaster sphcericus is 46 feet thick, and the 

 lowest bed is in places stained pink. At the top the Belemnite 

 marls are well marked, enclosing a medial bed of hard smooth 

 white chalk. 



Middle Chalk. At the base of this stage there is always a 

 certain thickness of hard nodular chalk which forms a great con- 

 trast to the soft marl on which it rests ; this rocky chalk is called 

 the Melbourn rock from a village in Cambridgeshire. 



Commencing as before in Kent, we find a good section of this 

 stage in the cliffs near Dover, which show : 



Feet. 



j t fRather rough lumpy white chalk .... 20 

 , ? . ,. I Smooth white chalk with thin layers of crey marl 

 Terebratuhnal and Mver al courses of flints . . . .90 

 t White chalk with seams of marl but no flints . CO 



Zone of /Hard chalk with frequent nodular layers . . 38 

 Rh. Cuvieri \Hard and rough nodular chalk .... 32 



~240 



