258 THE OLDEST AIR-BREATHERS 



earth had passed away before the land became the abode 

 of any large number and variety of animals ; while it was only 

 about the same time that the development of the vegetable 

 kingdom became so complete as to afford food and shelter 

 for air-breathers. 



It is also worthy of note that it is only in comparatively 

 recent times that we have been able to discover the oldest 

 air-breathing animals, and geologists long believed that the 

 time when animals had existed on the land was even shorter 

 than it had actually been. This arose in part from the in- 

 frequency and rarity of preservation of the remains of the 

 earliest creatures of this kind, and perhaps partly from the 

 fact that collectors were not looking for them. 



That there was dry land, even in the Cambro-Silurian 

 period, we know, and can even trace its former shores. In 

 Canada our old Laurentian coast extends for more than a 

 thousand miles, from Labrador to Lake Superior, marking the 

 southern border of the nucleus of the American continent in 

 the Cambrian and Cambro-Silurian periods. Along a great 

 part of this ancient coast we have the sand flats of the Potsdam 

 Sandstone, affording very favourable conditions for the im- 

 bedding of land animals, did these exist; still, notwithstanding 

 the zealous explorations of the Geological Survey, and of many 

 amateurs, no trace of an air-breather has been found. I have 

 myself followed the oldest Palaeozoic beds up to their ancient 

 limits in some localities, and collected the shells which the 

 waves had dashed on the beach, and have seen under the 

 Cambro-Silurian beds the old pre-Cambrian rocks pitted and 

 indented with weather marks, showing that this shore was then 

 gradually subsiding ; yet the record of the rocks was totally 

 silent as to the animals that may have trod the shore, or the 

 trees that may have waved over it. All that can be said is 

 that the sun shone, the rain fell, and the wind blew as it does 

 now, and that the sea abounded in living creatures. The eyes 



