102 



UPPER SECONDARY ROCKS. 



of them now present ; so that we have here, also, 

 decisive evidence that they have been elevated sub- 

 sequent to their deposition." 



Oolite. 



The rocks lying immediately above the new red 

 sandstone are called the oolitic. They derive their 

 name from the small rounded globules that are im- 

 bedded in them ; and as these sometimes resemble 

 the roes of fish, the rock is called roe-stone. This 

 formation abounds on the Continent of Europe, and 

 particularly in England ; although we meet with 

 limestone rocks in this country which have an oolitic 

 structure, it is yet in dispute whether they are ex- 

 actly equivalent to the European oolite, either as 

 respects their relative position or their organic re- 

 mains. According to Conybeare and Philips, the 

 oolitic group may be divided into three series, each 

 of which is composed of three distinct formations, 

 viz., an oolitic rock, a calcareous sandstone, and a. marl. 

 The oolite rocks are distinguished as upper, middle, 

 and lower, and occupy, in England, a zone which is 

 nearly 30 miles in average breadth, and extends 

 across the island from Yorkshire on the northeast 

 to Dorsetshire on the southwest. These again are 

 subdivided into several varieties, such as Portland 

 stone, Kimmeridge clay, Coral rag, Oxford clay, &c. ; 

 and below the whole is situated the formation called 

 lias. This term is derived from the provincial pro- 

 nunciation of the word layers; as the strata of lias 

 limestone are generally very regular and flat, and 

 can easily be raised in slabs from the quarry. When 

 the lias beds are fully developed, with their associ- 

 ated beds of clay, they form a mass of stratified 

 limestone and clay several hundred feet in thick- 

 ness, which rests upon the red marl described in 

 the last chapter. This lias limestone is of a dark 

 gray or yellowish white colour; argillaceous; divi- 

 ded into thin strata of an earthy, marly texture, and 



