178 



CHAPTER XII. 



ON THE LIAS AND OOLITIC SERIES. 



Geological Position of Lias Clay and Limestone. — Their mineral Characters. — 

 Alum-Slate in Lias.— Remarkable Organic Remains and Characteristic Fos- 

 sils. — Extent of the Lias Formation in England. — Interesting Junctions of Lias 

 and Red Marl. — Lias of France and the Alps. — Oolite or Roestone, the Jura 

 Limestone of Foreign Geologists. — Mineral Characters, and remarkable Or- 

 ganic Remains. — Lower Oolite. — Oxford or Clunch Clay.— Middle Oolites.— 

 Kimmeridge Clay. — Upper or Portland Oolites. — Stonesfield Slate with Or- 

 ganic Remains of Insects, Birds, Flying Reptiles, and small Land Q.uadrupeds. 

 — Extent of the Oolite Formation in England, and its abrupt Termination. — 

 Sections of the Oolitic Series of Beds in Yorkshire and the West of England, 

 compared with a Section of the Secondary Strata in Germany. 



The great bed of dark grey argillaceous limestone, divided into 

 thin strata (and associated with beds of clay) called Lias, is the best 

 characterized of all the secondary strata (except chalk), both by its 

 mineral characters and the fossil remains imbedded in it ; and it pre- 

 sents the same characters through a considerable part of France and 

 Germany. 



The geologist who has taken a comprehensive view of different 

 rock formations, and has compared the resemblance as well as the 

 diversity they present, must frequently have observed a tendency in 

 nature to reproduce similar strata in distant parts of a series of strata, 

 and even in different formations. In the chapter on the Coal Meas- 

 ures, I have given examples of the repeated recurrence of similar 

 strata at different depths, implying a recurrence of the same condi- 

 tions under which each had been formed. 



In the lowest part of the magnesian limestone in the northern coun- 

 ties, there are thin strata of marly limestone, called by Professor 

 Sedgwick Marl-slate, which may be regarded as the first approach to 

 a formation, resembling lias in many of its characters. Again, over 

 the middle beds of the sandstone there occurs a considerable thick- 

 ness of strata, in many respects resembling lias, called the Muschel- 

 kalk ; it may, perhaps, when viewed on a large scale, be considered 

 as a lower formation of lias, separated from it by the variegated marls 

 of the upper red sandstone. This bed, as before stated, has not been 

 discovered in England. The lias, therefore, cannot be mistaken for 

 any of the lower strata ; it serves as a key to the geology of the se- 

 condary formations in England ; and the first enquiry which the stu- 

 dent siiould make, when he is in doubt respecting the position of any 

 of the secondary beds, should be, Does it occur above or below the 

 lias "I 



The name Lias was probably given to this formation by the pro- 

 vincial pronunciation of the word layers, as the strata of lias limestone 



