i6 



THE CHAIN OF LIFE. 



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resisting rocks can be best seen as impressed moulds on tlie 

 weathered surfaces. 



Lastly, we sometimes have impressions or footprints repre- 

 senting the locomotion of fossil animals, rather than the fossils 

 themselves. In this way some extinct creatures are known to 

 us only by their footsteps on sand or clay, once soft, but now 



hardened into stone; and 

 in the case of some of the 

 lower animals the trails thus 

 made are often not easily 

 interpreted (Figs. 12, 12a). 

 It has been found that even 

 sea-weeds drifted by the tide 

 make impressions of this 

 kind, which, when they occur 

 in old rocks, are very mys- 

 terious. Even rain-drops are 

 capable of being permanently 

 impressed on rocks, and con- 

 stitute a kind of fossils. Be- 

 sides these we have many 

 kinds of imitative markings 

 which simulate fossils, as 

 those of concretions or no- 

 dules, which are often very 

 fantastic in shape, those 01 

 dendritic crystallisation giv- 

 ing moss - like forms, and 

 the complicated tracery pro- 

 duced on muddy shores by the little rills of water which follow 

 the receding tide (Fig. 13). Such things are often mistaken 

 by the ignorant for fossil remains, but are easily distinguished 

 by a practised eye. 



The reader who has followed these, perhaps somewhat dry, 

 details, will be rewarded for his patience by having some 



Fig. II. — Cast of erect tree {Sii^illaria) in 

 sandstone, standing on a small bed of 

 coal, South Joggins, Nova Scotia (Daw- 

 son's Acadian Geology). 



