ANIMALS OF LONG AGO 345 



preserved in the deposits of the world; the merest traces of lowly 

 organisms in the Archaean ; the invertebrates, crustaceans and worms 

 of the Cambrian, Ordovician and lower Silurian ; the armoured 

 fishes of the Devonian ; the amphibia of the later Carboniferous, 

 Permian and Triassic ; the reptiles of the Secondary Epoch, and the 

 mammals of Tertiary age and more recent times. The mammal is a 

 late arrival upon the arena of existence, but it has the elements of 

 victory in its composition, and has come to stay. 



The Quaternary Epoch, succeeding the Tertiary, is also called 

 Pleistocene, meaning most recent, and obviously its rocks and 

 deposits bear fossil remains of a comparatively recent flora and fauna. 

 The strata are said to be some 200 feet thick. 



CREATURES OF THE PAST.— Having presented the reader with 

 a cursory survey of the world's sedimentary deposits and given a 

 general idea of their extent and typical fossil remains, an attempt 

 will now be made to describe in greater detail some of the creatures 

 of long ago. A beginning will be made with the Amphibians, 

 and to do this we must go back in imagination to the period in 

 Palaeozoic time when the coal deposits were in process of formation. 

 The seams of coal, often buried hundreds of feet below the surface 

 of the earth, are evidences of old land surfaces which have gradually 

 subsided, and their vegetation has been covered with mud and sand 

 ultimately transformed into shale and sandstone. Seams of coal 

 lie in succession one above another with intervals of shale and 

 sandstone. As the Carboniferous land-surfaces subsided and were 

 covered with mud and sand, there were halts in the process of subsi- 

 dence, and during these halts fresh vegetation sprang up, flourished 

 and perished, in course of time to sink below the level of surround- 

 ing land and to be covered with sediment at the bottom of a marsh 

 or lake. Ultimately the vegetable remains, mingled perhaps with 

 those of fish, scorpions, etc., were converted through pressure and 

 other agencies into coal. The coal measure land-surface bore curious 

 plant life. There were forests of giant horsetails, club-mosses and 

 tree-ferns growing in a humid, warm atmosphere in damp ground 

 beside shallow seas and lakes. The land was intersected by rivers 

 carrying in suspension the debris of older rocks broken up by water, 

 chemical action and other denuding agencies. This material was 

 deposited in banks, in lakes and seas, and in course of time silted 

 them up, making new land-surfaces to be invaded by vegetation. 

 Animal life must have been abundant, although much of it has left 



