346 GEOLOGY 



The General Progress of Ordovician Life. 



While there was a fair preservation of the life of the Cambrian, 

 there is a much superior representation of the Ordovician life. Some 

 part of this is due to a real advance in fossilizable forms, and probably 

 to a real multiplication of their numbers, but a part is probably also 

 due to better conditions of preservation. The Ordovician life is prob- 

 ably to be regarded as the climax of the life of the first great fossil- 

 iferous period, and as such its fossils may well receive more study 

 and fuller illustration relatively than it will be possible to give later 

 faunas. 



The Scantiness of the Record of Land Life. 



Theoretically, there are strong reasons for believing that the pteri- 

 dophytes and perhaps other leading groups of plants clothed the land, 

 for they appear in abundance, in high development, and in wide differ- 

 entiation in the Devonian period. The physical argument for a vegetal 

 clothing of the land is also now stronger than before, for animal life 

 swarmed about the shores, and limestone was sometimes laid down 

 close to the Archean crystalline rocks and even among the granite 

 hills, as in Ontario and elsewhere. This is difficult to understand if 

 the crystalline rocks were naked and the wash from them unrestrained, 

 even if their surfaces were rather low. Rather should we expect arkose 

 sandstones in all the adjacent tract and relative scantiness of life, 

 because the land waters would be poor in organic matter if the land 

 bore no vegetation. If on the other hand the land were clothed with 

 vegetation and relatively low, silty wash would be limited, the land 

 waters rich in organic matter, and the conditions favorable at once 

 for teeming life near the shores, and free limestone deposition as a 

 consequence. But the record merely furnishes some imperfect relics 

 that are interpretable as land plants, without revealing much of the 

 land vegetation. 1 



The first record of insect life. — The oldest relic of insect life known 

 at present is a rather obscure wing found in the graptolite shales 

 of the Upper Ordovician of Sweden. It is referred to the order of 

 Hemiptera (bugs, cicada, etc.). Not enough is preserved to show 

 fully the insect's nature, but the existence of any flying insect of this 



1 Dawson, Plant Life, p. 21. 



