THE OOLITIC SYSTEM. 



719 



rains, and continued burning for a considerable time. This has, more recently, been 

 the case with a hill near Wey mouth, composed of bituminous clay with pyrites ; and, 

 upon a part of the cliff at Whitby falling, so as to become exposed to the action of the 

 tide, it took fire spontaneously, and continued to burn for two or three years. The 

 external aspect of lias districts in England exhibits plains diversified with low ridges 

 and broad river valleys, though it sometimes forms cliffs and steep escarpments, but of 

 no great elevation. The term is supposed to be a corruption of the word layers, alluding 

 to the unequivocal stratification displayed ; but in the annals of French geology it bears 

 also the name of calcaire a gryphee arquee, from a deeply incurved bivalve shell which 

 abounds in it, and is frequently met with in the English lias. The shells of this 

 deposit are very numerous, and present a variety of interesting and beautiful forms, of 

 which the following are examples. 



Gryphaea arcuata. 



Pecten lugdunensis. 



Spirifer Walcoti. 



Among the organic remains of the lias we have molluscous animals, Ammonites and 



Belemnites, of common occurrence, and of various species. 



The large family of Ammonites runs through all the fossiliferous formations, from the 



silurian to the chalk. With the latter the race became extinct. A notice of the genus 



has been deferred to this place because the number of species is by far the most abund- 

 ant in rocks of the oolitic 

 system. Of 223 species, 

 according to Phillips, 17 

 belong to the oldest fos- 

 siliferous rocks, 7 to the 

 carboniferous system, 15 

 to the new red sandstone, 

 137 to the oolite, and 47 

 to the chalk. The name 

 is derived from a fancied 

 resemblance of the shell 

 to the sculptured horn on 

 the head of Jupiter Arn- 

 mon. The shells are of 

 various sizes, from the 

 diameter of half an inch 

 to that of four feet. Two 

 species common to the 

 lias, Ammonites Buck- 

 landi, Ammonites Wal- 

 coti, are represented above, 



with one, Ammonites nudosus, belonging to a limestone in France of the new recUand- 



stone era, and another, Ammonites varians, from the chalk. 



Ammonites Bucklandi. 



A. Walcoti. 



A. imdosus. 



A. varians. 



The Ammonites Walcoti 



