CRETACEOUS FORMATION. 



67 



times only in masses agglutinated to each other by mud and sand ; 

 sometimes it is entirely wanting. Above it are clays which con- 

 tain, often in great quantity, ex'ogy'ra (Jig. 115), and oysters, 

 among which is distinguished the great species, named Ostrea 

 Leymerii; the Lima elegans (Jig. 116) is also found. Among 

 these clays are met large calcareous masses, a good deal flattened, 

 filled with the same fossil shells, presenting lumachella* or conchi- 

 lians, which have been confounded with the Portland group, form- 

 ed by an accumulation of the ex'ogy'ra vi'rgula (Jig. 109). Next 

 we have, at least in parts of France, sands and clays, sometimes 

 variegated in colours, among which are masses of iron ore, com- 

 monly o'olitic. The remains of shells seem to give place here to 

 ferruginous masses. 



3. These last deposits seem to be wanting in other localities, in 

 which we find, instead, great layers of limestone, more or less 

 compact, sometimes white, sometimes coloured, which enclose 

 hippuri'tes,spheruli'tes,and even nummuli'tes, which have been long 

 regarded as belonging to the 



tertiary formation. We also 

 find here a fossil which is 

 very characteristic ; it was at 

 first compared to the diceras 

 (Jig. 106), but is now call- 

 ed Chama ammonia (Jig. 

 117). This species of shell, 

 which is often very abundant, 

 is always so imbedded in the 

 mass of rock, where it is dis- 

 tinguished by the sinuosities Fi S- m.Cha'ma ammo'nia. 

 it forms, that it is very difficult to detach it entire. Various spe- 

 cies of ammonites, gigantic hamites, several species of Crio'ceratitei 

 (Jig. 118 from the Greek, Krios, 

 a ram, and Keras, horn) and belem- 

 nites. The trigo'nise, which are still 

 met with and continued to the green- 

 sand, present here new species (Jig. 

 119), which seem to be characteris- 

 tic. 



4. In the south of France and in 



the Pyrenees the chalk formation Fig , u8.-Cri'oceratue S uvaiiii. 



* Lumachella an Italian word, formed from limacea, a snail, which is 

 derived from the Latin, Umax. The word is used to designate a mass 

 formed of the remains of snails, &c. with their nacre, united by gluten 

 It is also called conchilian marble. 



3. Are sands and clays everywhere found above the yellowish limestone f 

 What fossils are found in these limestones of the cre'a'ceous group? 



27 



