FOSSILS. 



73 



Fig. 134. A mmonites rothomage' nsit 



Fig. 135.Ex'ogy'ra columba. Fig. 137. Terebra' tula octo'plica'ta. 



^Nu'cula (from the Latin, nux, a nut) is an inequilateral bivalve shell; the 

 hinge is narrow, and has many teeth like those of a comb : several species 

 are known. 



Scaphi'tes-(from the Greek, scaphe, a boat) is an eliptical, many cham 

 bered shell, somewhat resembling- the ammonites.- 



Ba'culites (from the Latin, ba'culwn, a stick) is a multilocular, straight, 

 or slightly bent, and slightly conical shell; the chambers are separated 'by 

 septa, pierced by a marginal siphuncle. 



Turrili'tp.s is a spiral, turriculated, multilocular shell; the chambers are 

 separated by winding septa, which have the si'phuncle in their disks : the 

 aperture is round. This fossil must not be confounded with the Turrite'lla, 

 which is a univalve, found both recent and fossil. 



15. The Upper Chalk Formation. In- this we find chalk with 

 and without flints. The layers of flint" are frequently almost the 

 only indications of stratification afforded by the mass. It is fre- 

 quently soft, and susceptible of solution or suspension, as in Spa- 

 nish whiting, which contains an immense quantity of microscopic 

 shells, belonging to the group of foraminifera. In some cases it 

 is arena'ceous, and sometimes very compact. Although often 

 white, we find it in some places coloured grey, yellow, red, &c. ; 



15 How is the upper chalk formation characterized ? 



