242 GEOLOGY OF THE ISLE OF WIGHT. 



contributes greatly to the picturesque character of 

 the local scenery.* 



The layers and concretionary masses of chert are 

 principally distributed in the upper part of the 

 series ; and beneath them are sands, and a bed of 

 sandstone from two to four feet thick, which, 

 though soft when first extracted, hardens by expo- 

 sure to the air, and becomes an excellent building 

 material. The ancient churches on the south 

 side of the Island have been constructed of this 

 stone, and it is being largely quarried for the 

 edifices now in progress of erection. 



Fossils of the Firestone strata. — The fossils 

 of the arenaceous and cherty strata of the firestone 

 group, comprise many species which also occur in 

 the uppermost deposit, the chalk marl; and like- 

 wise several that have either not been observed, or 

 are very rare in the other strata. They consist of 

 several kinds of Ammonites, Nautili, Hamites, 

 Scaphites, and other cephalopoda; numerous bi- 

 valves, especially pectens, terebratulae, trigoniw, 



* Captain Ibbetson, whose beautiful and accurate models of the Undercliff 

 are exhibited in the Polytechnic nstitution, subdivides the firestone group 

 into the following : — 1. Upper greensand ; 2. Chloriticmarl ; ','>. Second bed of 



eenBand; 1. Fossiliferous war!, in which large scaphites occur; 5. Two 

 alternations of malm and rag: the term malm is applied to a firm argillaceous 

 rock, and raff, to the cherty sandstone that alternates with the former. A 

 very large collection, comprising numerous species of shells, zoophytes, &c, 

 i Obtained from these strata, and especially from the fossiliferous 

 marl. 



