20 PAL^EONTOLOGICAL BOTANY. 



warm climates, liave representatives at great elevations, as 

 Oncidium nubigenum at 14,000 feet in the Andes, and Epi- 

 dendrum frigidimi at from 12,000 to 13,000 feet in the 

 Columbia momitains. These facts point out the care neces- 

 sary before drawing conclusions as to the climate which fossil 

 plants may be supposed to indicate. 



FOSSILIFEROUS RoCKS. 



The rocks of which the globe is composed are divided into 

 two great classes- — the Stratified or Aqueous, and the Unstra- 

 tified or Igneous. The stratified rocks frequently contain fossil 

 remains, and are then called fossiliferous ; those with no such 

 remains are designated non-fossiliferous or azoic. The igneous 

 unstratified rocks, included under the names of Granitic and 

 Trappean, show no appearance of animal or vegetable remains. 

 Those trap rocks, however, which have been formed of loose 

 volcanic ashes have often enclosed and preserved the remains 

 of plants and animals ; while even between the successive 

 beds of old lava-like trap rocks organic remains are some- 

 times found. Thus, in Antrim, near the Giant's Causeway, 

 deposits containing vegetable remains occur inter-stratified 

 with basaltic rocks. These remains are of miocene age, 

 and have been referred to coniferous plants, beeches, oaks, 

 plane trees, etc. Similar plants have been discovered in 

 a similar position by the Duke of Argyll in the island of 

 Mull. In trap rocks near Edinburgh, lignite with distinct 

 structure has also been detected. Silicified wood and coal, 

 imbedded in trap rocks, have been seen in Kerguelen's Land. 

 The wood is found enclosed in basalt, whilst the coal crops 

 out in ravines, in close contact with the overlying porphyritic 

 and amygdaloidal greenstone. Hooker has also seen silicified 

 wood, in connection with trap, in Macquarrie's Plains, in 

 Tasmania. Several beds of trap-tuff or ash, formed into 



