164 De Ranee — On the Albian, or Gault of Folkestone. 



following terms have been used by the writer of this paper as being 

 more uniform with it : — 



Danian Stage =: Upper Chalk. 



Zone of =: Chalk rock. 



Upper Turonian sub-stage =Lower Chalk. 



Zone of Belemnitella mucronata disjunction led. 



Lower Turonian sub-stage =Grey Chalk. 



Zone of Scaphites oiqualis = Chloritic Marl. 



Cenomanian stage =Upper Greensand. 



Upper Albian sub-stage =:Upper Gault. 



Zone of Am. Beudantii z=. Nodule hed. 



Lower Albian sub-stage =Lower Gault. 



Zone of Am, interruptus -zziJunction led. 



Upper Aptian := Folkestone beds. 



Zone of Rhynchonella sulcata ■ztl Junction hed. 



Middle Aptian =Sandgate beds. 



Zone of Terelratula ohlonga =iJunction led. 



Lower Aptian sub-stage =Hythe beds. 



Lower Neocomian sub-stage r=Atherfield Clay. 

 A •' true 'junction bed' represents in a tangible form the actual break 

 in organic life between two stages, and either introduces a new 

 fauna altogether, as Bed xi., separating the Aptian from the Albian 

 stages ; or contains a ' limit fauna,' as Bed iv., dividing the Upper 

 from the Lower Albian sub-stages. Some species have an extremely 

 limited vertical range in a stage or sub-stage, and yet reappear in 

 other stages, producing the phenomenon of recurrent forms and 

 horizons." Thus there are two distinct horizons of Peden asper in 

 the Albian of Kent, and another in the first foot of Greensand below 

 the Chloritic Marl or Zone of Scaphites ^qualis at Beaminster and 

 Chardstock. As an assemblage of horizons of similar range constitute 

 a zone, a recurrence of several horizons defines or marks a recurrent 

 zone, which, as above stated, appears to occur at every return of similar 

 physical conditions. The junction beds between all the stages and 

 sub-stages of the Cretaceous are examples of this, for they contain in 

 addition to the " initiative " or " limit" fauna, as the case may be, a 

 large percentage of forms peculiar to themselves, thus the reptile 

 Icthyosaurus campylodon is found in every junction zone, from the 

 zone of Bhjnchonella sulcata, between the Upper and Middle Aptian 

 (Folkestone and Sandgate beds), to the zone oi Belemnitella mucronata, 

 between the Upper and Lower Turonian (Lower and Grey Chalks). 

 Many other species occur in a similar manner ; Solarium conoideum, 

 which is limited to the upper three feet of the zone of Ammonites 

 Beudantii (between the Upper and Lower Albian), even reappearing 

 in the zone of Scaphites cequalis and Am. varians (Chloritic Marl) at 

 Cambridge. Associated with these recurrent species, in every junction 

 bed, are found phosphatic nodules, those from the Albian beds iv, 

 and XI. are rich in phosphates and contain sulphuret of iron, silica, 

 and lime, the phosphatic matter appears to have been deposited in a 

 decomposed or gelatinous state, for it often entirely surrounds shells, 

 bones, bored wood, and Crustacea, sometimes entangled with and 



