252 C. E. De Ranee — Deposition of Cretaceous Strata. 



place when the area of change was coincident, to or greater than the 

 area of habitat of that species. The longer time elapsing during the 

 period of change, the greater chance would hardy species have of 

 becoming naturalized, and living in conditions as to quality of sea 

 bottom and depth differing from those they had been accustomed to, 

 and for migrating to more favourable areas. 



A comparison of many of the species occurring in the Phosphatic 

 seams of the Lower Greensand (Upper Neocomian of Kent) with 

 those from the junction bed " Am. interruptus Zone " of the Gault of 

 Folkestone, the " nodule bed " dividing the Lower and Upper Gault 

 of the same place, and with those of the zone of Scaphites cequalis 

 (Chloritic Marl) of Dorsetshire and Cambridge, shows a striking 

 number of species in common, and much resemblance in physical 

 aspect, — rolled and water-worn shells, drifted wood bored by shells, 

 rolled bones of Saurians, drifted pebbles, and masses of phosphatic 

 matter, which can sometimes be made out to be molluskite, probably 

 of large RostellaricB. 



The facies of the whole suggests a beach and shore deposit, which 

 is to a certain extent borne out by the habitats of the recent analogues 

 of the species of shells of molluscs found associated. The re- 

 currence of these species at the precise era of time when physical 

 conditions were changing would appear to indicate the continuance of 

 an old coast-line, from which the shells were washed by currents, 

 which coast-line would appear to have continued throughout the 

 whole period occupied by the whole of the Lower Cretaceous sj^stem 

 of the south of England. The reason why currents should have 

 flowed from this old land at the moment when physical changes 

 introduced changes of sediments is difficult to explain. Possibly 

 the presence of the molluskite may be due to large quantities of 

 freshwater coming down to this old coast-line, and killing large 

 quantities of mollusca, their bodies being floated away by tidal or 

 other currents. If the south-west of England was still land 

 during the deposition of the Neocomian beds, a portion of this old 

 coast may possibly have been in Somerset and Devon. 



List of species occurring in the Gault of Black Ven, Dorset ; 

 also those found at Golden Cap marked a ; those in the Folkestone 

 Gault h ; those in the Cow Stones c : 

 b, c. Hemiaster asterias, Forbes. 



a. Fecten quadricostatiis, Sby. 

 a. Fecten orbicularis, Sby. 



Gervillia Unguloides, Forbes. 

 a, b, c. Fnoceramiis concentricus, Park. 

 a, b, c. Finna tetragona, Sby. 



a, h. Lima parallela, Sby. 



b. CucullcEa carinata, Sby. 

 JLrca carinata, Sby. 



b. Venus tenera, Sby. 

 V. sublcevts, Sby. 



c. Fanopcea mandibula, Sby. 

 b, c. Fanopcea plicata, Sby. 



Cytherea truncata (?), Sby. 

 Solen Dupinianus, D'Orb. 

 Fholadomya Fabrina, Ag. 

 Nucula bivirgata, Sby. 



a. Nucula peetinata, Sby. 



b. N. ovata, Sby. 

 Thracia, n. sp. (?). 



b. ActcBon affinis, Sby. 



b. Cerithium tritnonite, Mich. 



b. Fusus rusticus (?), Sby. 



F. elegans, D'Orb. 

 b. F. olathratus, Sby. 

 b. Aporrhais Orbigniana, P. & E. 

 b. Natica GauUina, D'Orb. 

 b. Flerocera retusa, Sby. 



Tiirritella Vibrayeana, D'Orb. 

 b. Deutali'um decussatum, Sby. 



Scalaria Fitpiniana, D'Orb. 

 b, c. Ammonites splendens, Sby. 



Saurocephalus, sp. 



