THE STORY TOLD BY FOSSIL PLANTS 



to increase in size for many years and carry aloft an ever 

 larger canopy of leaves, and the development of seeds, which 

 are a much more efficient means of reproduction than the 

 simple single-celled spores of the lower plants. 



Geologists construct their history in much the same way 

 as any other historians, but instead of dealing with written 

 documents or the handiwork of man they deal with the 

 series of rocks that make up the crust of the earth, and 

 especially with the fossils preserved in the rocks — the remains 

 of the plants and animals that were alive when the rocks 

 were being deposited as mud or sand. (See geological time 

 table on page 160.) 



You might suppose that this record of the past would be 

 so scanty and broken that we could not read it. It is, indeed, 

 far from complete, but when we remember that even the 

 formation of a single bed of sandstone or of clay consumed 

 a long time we can see that innumerable plants and animals 

 might have been covered up by accumulating sediments and 

 so well preserved that we could use them in our study of 

 the earth's history. 



The earliest chapter of the world's organic history we call 

 the time of ancient life, or the Palaeozoic era, which is saying 

 the same thing in Greek. This Palaeozoic era we divide into 

 periods, each marked by distinctive types of fossils. The 

 names of the periods that make up the Palaeozoic era, given 

 in order from the oldest to the youngest, are Cambrian, 

 Ordovician, Silurian, Devonian, Carboniferous, and Permian. 

 Some of these names are geographical, each derived from 

 the name of some place where rocks of that age are exposed. 

 Cambrian is from Cambria, the Latin name of Wales; Silurian 

 is from the name of a tribe — the Silures — which in Roman 

 times inhabited that part of Britain where the Silurian rocks 



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