Ch. XXL] MINERAL CHARACTER OF THE LIAS. 41 5 



the strata, both of the Inferior Oolite ai d of the formations that 

 immediately succeed it." * 



Mr. Howell has pointed out that in Bedfordshire the Cornbrash 

 and Kelloway rocks are sometimes both absent, and the Oxford clay 

 rests conformably on the Great Oolite, showing, like the examples 

 before cited, that conformity is no proof of direct sequence, and 

 aiding us more and more to conceive that the changes in the organic 

 world may in reality have been gradual and uninterrupted, although 

 the fragmentary character of the records handed down to us might 

 lead us to infer, unless we were constantly on pur guard against 

 being deceived, that there had been many general and sudden breaks 

 in the recording process, and abrunt transitions from one set of 

 organic types to another. 



CHAPTER XXI. 



jurassic group, contiriued — lias. 



Mineral character of Lias — Numerous successive Zones in the Lias, marked by dis- 

 tinct fossils, without unconformity in the stratification, or change in the mineral 

 character of the deposits — Xame of Gryphite limestone — Fossil shells and fish — 

 Radiata — Ichthyodorulites — Reptiles of the Lias — Ichthyosaur and Plesiosaur — 

 Marine Reptile of the Galapagos Islands — Sudden destruction and burial of fos- 

 sil animals in Lias — Fluvio-marine beds in Gloucestershire, and insect limestone 

 — Fossil plants — Origin of the Oolite and Lias, and of alternating calcareous and 

 argillaceous formations. 



Lias. — The English provincial name of Lias has been very gen- 

 erally adopted for a formation of argillaceous limestone, marl, and 

 clay, which forms the base of the Oolite, and is classed by many 

 geologists as part of that group. They pass, indeed, into each other 

 in some places, qs near Bath, a sandy marl called the marlstone of 

 the Lias being interposed, and partaking of the mineral characters 

 of the lias and the inferior oolite. These last-mentioned divisions 

 have also some fossils in common, such as the Avicula inceqicivalvis 

 (fig. 435). Nevertheless the Lias may be traced throughout a great 

 part of Europe as a separate and independent group, of consider- 

 able thickness, varying from 500 to 1000 feet, containing many 

 peculiar fossils, and having a very uniform lithological aspect. 

 Although usually conformable to the oolite, it is sometimes, as in 

 the Jura, unconformable. In the environs of Lons-le-Saulnier, for 

 instance, in the department of Jura, the strata of Lias are inclined 



* Geol. Quart. Journ., vol. xx. p. 06. '1864. 



