THE HISTORY OF LIFE 149 



from 30 to 50 million years. The tendency is to in- 

 crease rather than decrease the estimate. It is quite 

 certain, however, that life existed for an immense period 

 prior to the Cambrian, though only very inadequate 

 remains have been discovered. The deficiency of fos- 

 sils in the earlier (Algonkian) deposits may be largely 

 due to the unsuitability of primitive types for preserva- 

 tion ; but more especially to the fact (as it seems to be) 

 that the early life existed in the sea, and the old shore 

 lines are now buried beneath the oceans or far below 

 the surface of the earth. Although great masses of 

 Algonkian rock have been studied, they appear to repre- 

 sent old land and fresh-water surfaces, where only very 

 primitive forms of plant life existed. These include 

 algae (water weeds of low type) and minute objects con- 

 sidered to be bacteria. Somewhere, some day, some 

 happy naturalist will perhaps discover an old Algonkian 

 shore deposit, with well-preserved animals much older 

 than any now known. 



6. Fpr our knowledge of Cambrian life we are espe- Life in 

 cially indebted to Dr. Charles D. Walcott of the Smith- 

 sonian Institution. Cambria is the old name of Wales, 

 where the Cambrian rocks were first described by the 

 English geologist, Adam Sedgwick ; but we now know 

 them from many different regions. The most remark- 

 able deposit of fossils was found by Dr. Walcott on the 

 mountain side above Field, in the Canadian Rockies. 

 Fragments picked up near the base of Mount Wapta 

 indicated that somewhere on the slope fossils would 

 be found in place. Following this clew, a quarry was 

 made at an altitude of 8000 feet above sea level, and 

 after the surface rock had been blasted out, a wonder- 

 ful series of remains was obtained. So perfect is the 

 preservation, that even such delicate objects as jelly- 



