THE AGE OF REPTILES 



to the rock a banded or ribbon-like appearance, which 

 may well cause the workmen to describe it as occurring 

 in " lyers. 11 



To the upper Jurassic beds, which contained much 

 more limestone and also occasional beds of sandstone, 

 the name of Oolite was given. The Oolitic strata have 

 a special interest for English geologists, for it was in 

 them that William Smith, the west of England sur- 

 veyor, first made out (about the year 1790) the order 

 of succession of the strata, and by this was led to his 

 great discovery that " strata could be identified by their 

 organic remains,"" that is by their fossils. He noticed 

 that some of the limestone beds of the strata we are 

 about to describe consisted of small rounded grains, 

 which made them resemble the roe of a fish indeed, 

 they were called " roestone " by the workmen. Hence 

 Smith when seeking a name for this set of strata 

 bethought himself of the term "Oolite, 11 which means 

 " egg-stone " (Gr. oora, an egg, and lithos, a stone). 

 Where the grains are very large the limestone is called 

 "pea-grit 11 or pisolite (Lat. pisum, a pea). Some beds 

 which contain numerous and irregularly shaped frag- 

 ments of shells, corals, etc., are called rag-stones. 



The Jurassic strata of Great Britain were sediments 

 laid down in warm seas surrounding an archipelago of 

 which Dartmoor, Wales, and Cumberland formed some 

 of the islands. The whole of Western Europe was 

 sinking and had sunk ; and the waters of the open 

 ocean were admitted into and mingled with the salt 

 mineral waters of the great Triassic lakes. The change 



238 



