OUTLINES OF GEOLOGY. 



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110. The fossils of this group bear a strong general re- 

 semblance to those of the chalk; that which is distinctive is 

 the genus gryphaea, (molluscous,) which does not appear to 

 occur in the chalk, and is here abundant. 



111. The green sand formation comes out from beneath 

 the chalk, in many parts of Europe. In the United States, 

 it forms a belt, on which the superior order rests, extending 

 from Sandy Hook to Georgia. 



112. The oolitic group, according to Coneybeare and 

 Philips, may be divided into three series, each of which is 

 composed of three distinct formations, viz. an oolitic rock, a 

 calcareous sand-stone, and a marl. The oolites are distin- 

 guished as upper, middle, and lower. The marls are called 

 in England, the Kimmeridge and Oxford clays, and Lias. 

 The latter is an indurated marl, varying in colour from light 

 gray to black. It may be used to form an hydraulic cement, 

 and in lithography. It is remarkable as the principal site of 

 the remains of extinct families of sauri, which differ mate- 

 rially from those which now exist. 



1 13. No more than a single family of terrestrial mamma- 

 lia has been found in this group, namely, one belonging to 

 the order marsupia. In other respects, the fossils approach 

 in character to those of the chalk, but are of different spe- 

 cies, and even those of the different series are not identical. 

 The family of belemnites, however, becomes more rare, and 

 that of ammonites more abundant. Of the extinct sauri 

 found in this group, and especially in the lias, the most re- 

 markable genera are : 



(1.) The megalosaurus, an animal uniting the stature of 

 an elephant to the proportions of a lizard, some of whose ske- 

 letons have been found 70 feet in length. The organization 

 of this animal would have enabled it to move on the land, 

 but its size must have confined it almost wholly to the water 



(2.) The Icthyosaurus, having four paddles, resembling in 



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