IBBETSON AND FORBES ON THE LOWER GREEN SAND. 191 



Crackers, is full of Gervillia aviculoides and other fossils, and a 

 similar stratum immediately above (the Upper Crackers) abounds 

 in fossils peculiar to itself ; indeed it is in this bed that most of 

 such of the species as are limited in their distribution, occur. The 

 Crackers occupy a thickness of 18 feet. 



A clay bed, 20 feet thick, having the properties of fullers' earth, 

 and similar in appearance to that preceding the Crackers, succeeds : 

 it is very fossiliferous, and, like the other, abounds in Crustacea, 

 mostly of species identical with those in the Lower Lobster Bed. 

 This is termed in the section the Upper Lobster Bed. Am- 

 monites and several bivalves accompany these Crustacea. 



A dark sandy clay succeeds, and is very fossiliferous ; the cha- 

 racters of the fossils do not for the most part differ from those in 

 the lowest clays. It is 20 feet thick. 



This is capped by a band of Terebratulae (mostly T. Gibbsii) 

 imbedded in the stratum of dark sand, 22 feet thick. The Tere- 

 bratulas are in immense abundance and accompanied by Serpulae. 



A series of beds containing zones of Gryphcea sinuata imbedded 

 in dark sand succeed. The Gryphasa zones mostly alternate with 

 rows of large nodules containing Crioceras and Scaphites. This 

 assemblage of Gryphaea zones is interrupted in the centre by a 

 bed of sandy clay, 34 feet thick, very fossiliferous, and in which a 

 great many of the fossils of the lower clays reappear. These 

 Gryphcea and Crioceras beds, with the included clays, have a 

 thickness of 155 feet. 



Thirty feet of dark sand, containing prolific zones of Terebratulas, 

 chiefly T. biplicata, succeed, and form the base of a new succession 

 of Gryphasa bands imbedded in dark sand; but the Crioceras 

 nodules are absent. Twenty-four feet is the extent of this upper- 

 most series of Gryphaea zones. 



Above this the beds become ferruginous, and are occasionally, 

 though rarely, mixed with dark blue clay. Fossils in some parts 

 are abundant, but mostly in the state of casts, and no new forms 

 appear. A lignite bed occurs in the lower part of these ferrugi- 

 nous beds, the lignites being arranged in zones. There are also 

 here and there rows of calcareous concretions, usually of an oblong 

 shape, and mostly having a direction towards the S.E., like the 

 lines of oblique bedding occasionally presented in this part of 

 the series. 



At the top of Black-Gang-Chine waterfall, a series of indurated 

 ferruginous sand rocks alternating with dark sandy clays appear. 

 The sand rocks are composed of quartz grains, and exhibit lines of 

 oblique bedding. They contain no fossils. 



At the uppermost part of the Lower Green Sand is a series of 

 thin beds, alternately ferruginous and sand, lying immediately 

 below the gault. Casts of a Solarium (species unknown), and of 

 an Ammonite, were found in these bands. 



§ 2. Grouping of the Strata. 



The 63 strata enumerated may be grouped under three divisions, 

 from their general mineral character. 



