^Ixxviii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxxix, 



If the vegetation of the land arose like Aphrodite from the sea, 

 it is conceivable that, on the first emergence of the foundations of 

 "the continents, the plants transferred from water to land had not 

 reached a stage of evolution consistent with adaptation to the new 

 environment. Moreover, as we have seen, it is probable that in 

 ■some Archaean regions the conditions were not favourable to plant- 

 clevelopment. The customary assumption is that life in the 

 Archaean Era was represented by simple forms ill adapted for 

 preservation. The lower branches of genealogical trees are traced 

 back in imagination to a period of which we have no records fit to 

 -serve as foundations : the geologist and the palaeobotanist usurp 

 ~khe functions of the poet : 



' And as imagination bodies forth 

 The forms of things unknown, the poet's pen 

 Turns them to shapes, and gives to airy nothing 

 A local habitation and a name.' 



The Cambrian, Ordovician, and Silurian Periods. 



The outstanding feature of the Cambrian Period is the abund- 

 ance of marine sediments, formed both in shallow and in compara- 

 'tively deep water. The extraordinary wealth of the Cambrian 

 fauna, in contrast to the barrenness of the underlying Archaean 

 strata, is illustrated with especial vividness by the remarkable 

 collection of marine fossils described by Dr. C. D. Walcott from 

 Middle Cambrian rocks in Montana and British Columbia more 

 than 6000 feet below the upper limit of the Cambrian S} T stem. 

 The animals of the Cambrian seas have been described as ' most 

 intensely modern ', and as ' belonging to the same order of nature 

 as that which jDrevails to-day '. The meagreness of the botanical 

 records precludes any general statement as to the nature of the 

 marine vegetation. In consideration of the absence of any well- 

 defined distinction between the plants recorded from the several 

 Lower Palaeozoic systems, and in order that time may be allowed 

 for the inclusion in this very incomplete sketch of some account 

 of the land-vegetation of the Devonian Period, the Cambrian, 

 'Ordovician, and Silurian Periods will be reviewed together. The 

 Ordovician sea trangressed over part of the Cambrian land, and, 

 in the clearer waters, beds of limestone, extending as far north as 

 Arctic Alaska, were built up, in part at least, of the calcareous 

 skeletons of animals and plants. But the rocks give no clue to 

 the nature of the pioneers of a land-flora. 



