LIFE 



37 



upon our planet. Almost all the great types of invertebrates are 

 already present and very definitely characterized, indicating that 

 life had been differentiating for a vast period before the lowest 

 Cambrian rocks had been laid down. As compared with the 

 faunas of other Palaeozoic periods, that of the Cambrian is very 

 scanty, but our knowledge of it has been greatly increased of 

 late and may be expected to increase in the future. 



Though the successive Cambrian faunas have a very uniform 

 distribution over wide areas, there are already indications of local 

 differences which mark out faunal provinces ; thus, the Middle 

 Cambrian fossils of Newfoundland are more similar to those of 

 Europe than to those of the Appalachian and interior regions of 

 America. The same fauna recurs in Alabama, but not further 

 north in the Appalachians. The advance of the sea gave to Upper 

 Cambrian life a wider and more uniform distribution over the 

 continent than to that of the Lower. 



Of Plants nothing is surely known; certain marks on the 

 bedding planes of strata have been regarded as seaweeds, but 

 they are too obscure for determination. 



The fauna is principally made up of Brachiopods and Trilobites, 

 but many other types are represented also. 



Spongida. — Siliceous Sponges are not uncommon. 



Coelenterata. — The Hydrozoa are believed to be represented 

 by the Graptolites, a series of forms which are confined to the 

 older Palaeozoic rocks. These curious animals formed compound 

 colonies, with cells for the different individuals arranged on one 

 or more sides of a stem, and of a great variety of form ; some 

 are straight, others spiral, and though commonly found in single 

 branches, some specimens have many branches united. (See 

 PI. II, Fig. 3, p. 383.) The skeleton was horny, and so the fossils 

 appear as mere markings on the rocks, but often in excellent pres- 

 ervation. The systematic position of the Graptolites is entirely 

 uncertain, though they are usually referred to the Hydrozoa. 



Other Hydrozoa are the jelly-fish, of which recognizable casts 

 have been found in large numbers. 



It is still a question whether Corals were present in the Cam- 



