328 



FOSSIL PLANTS. 



[Ch. XXI 



Nat. size. 

 Wing of a neuropterous insect, from 

 the Lo^vel• Lias, Gloucestershire, 

 (Kev. P. B. Brodie.) 



feet in this bed. Ferns, with leaves of mo- 

 nocotyledouous plants, and some apparently 

 brackish and freshwater shells, accompany 

 the insects in several places, while in others 

 marine shells predominate, the fossils varying 

 apparently as we examine the bed nearer or 

 farther from the ancient land, or the sourco 

 whence the freshwater was derived. There are two, or even three, bands 

 of " insect limestone" in several sections, and they have been ascertained 

 by Mr. Brodie to retain the same lithological and zoological characters 

 when traced from the centre of Warwickshire to the borders of the 

 southern part of Wales. After studying 300 specimens of these insects 

 from the lias, Mr. Westwood declares that they comprise both wood- 

 eating and herb-devouring beetles of the Linnean genera Elater^ Cara- 

 bus, &c., besides grasshoppers (^Gryllus)^ and c'.'etached wings of dragon- 

 flies and may-flies, or insects referable to the Linnean genera Lihellula^ 

 Ephemera^ Hemerohius^ and Panorpa, in all belonging to no less than 

 twenty-four famihes. The size of the species is usually small, and such 

 as taken alone would imply a temperate climate ; but many of the as- 

 sociated oro-anic remains of other classes must lead to a different conclu- 



o 



sion. 



Fossil plants. — Among the vegetable remains of the Lias, several 

 species of Zamia have been found at Lyme Regis, and the I'emains of 

 coniferous plants at Whitby. Fragments of 

 wood are common, and often converted into 

 limestone. That some of this wood, though 

 now petrified, was soft when it first lay at 

 the bottom of the sea, is shown by a speci- 

 men now in the museum of the Geological 

 Society (see fig. 420), which has the form 

 of an ammonite indented on its surface. 

 M. Ad. Brongniart enumerates forty-seven liassic acrogens, most of 

 them ferns ; and fifty gymnogens, of which thirty-nine are cycads, and 

 eleven conifers. Among the cycads the predominance of Zamites and 

 Nilsonia, and among the ferns the numerous genera with leaves having 

 reticulated veins (as in fig. 385, p. 314), are mentioned as botanical 

 characteristics of this era."^ The absence as yet from the Lias and Oolite 

 of all signs of dicotyledonous angiosperms is worthy of notice. The leaves 

 of such plants are frequent in tertiary strata, and occur in the Cretaceous, 

 though less plentifully (see above, p. 266). The angiosperms seem, there- 

 fore, to have been at the least comparatively rare in these older secondary 

 periods, when more space was occupied by the Cycads and Conifers. 



Origin of the Oolite and Lias. — If we now endeavor to restore, in 

 imagination, the ancient condition of the European area at the period of 

 the Oolite and Lias, we must conceive a sea in which the growth of 



Fig. 420. 



* Tableau des Veg. Fos. 1849, p. 105 



