BIIODIE— GEOLOGY OF GLOUCESTERSHIRE. 



373 



Plesiosaurus differed from tlie Iclithjosaurus in its long, swan-likc neck, in 

 its extended paddles, short tail, and small head, which it must have raised 

 high above the water like a swan's ; and although a carnivorous reptile, 

 it was altogether unable to cope with the Iclithjosaurus, its most dreaded 

 foe. Both these genera v/ere covered with a tough smooth skin, and 

 not with scales, as we might have imagined ; and this we know from the 

 discover}^ of a portion of the skin attached to the skeleton of an 

 Iclithjosaurus, from the Lower Lias at Barrow-on-Soar, in Leicester- 

 shire. 



The student must not expect to obtain a perfect specimen of one of 

 these reptiles without considerable labour and perseverance; for when 

 one is found entire, much skill and patience is required to clear away 

 the hard matrix which surrounds it, and many an hour has to be devoted 

 to the development of even a single bone ; and some knowledge of its 

 anatomy also is requisite, especially when, as it often happens, a 

 specimen has been broken up into innumerable and disjointed fragments, 

 which all have to be correctly united before a full restoration of the 

 original can be completed. In this way Cuvier and Owen have restored 

 the entire skeleton of several extinct animals, even from heaps of bones 

 piled together as in a charnel-house ; so that magically, as it were, at 

 the bidding of the comparative anatomist, each bone has assumed its 

 right place, and from its internal skeleton, thus remodelled, the external 

 form and habits of the creature as living have been fairly demonstrated. 

 It is, indeed, a wonderful power which God has thus given to man, as 

 the reward of patient study and anxious thought, thus to rebuild the 

 creatures of the past. 



The strata in which these saurians are met with are not usually rich 

 in other fossil remains, though the surface of the limestone is sometimes 

 crowded with Modiola minima, and small oysters; and at Erockeridge 

 Common the blue strata are charged with Ammonites pJaiiorlis, which 

 often retains the nacreous pearly material of the shell, givirg it a very 

 beautiful appearance, like opal. The total thickness of this part of the 

 series is about fifteen feet, having a dip of fifteen degrees to the east at 

 Dcfford and at Brockeridge. The entire thickness of the Lower Lias is 

 very considerable, quite six hundred feet, or even more, but much less 

 in the south and south-east districts. 



We have now arrived, in descending order, at the basement-beds" 

 of tho Lias, the lowest of which rest immediately on the Eed Marl, 



