50 RELICS OF PRIMEVAL LIFE 



preserved. In addition to biological arguments 

 in favour of this view, there is the fact that some 

 of the beds are stained with carbonaceous or coaly 

 matter, as if the sediment had been mixed with 

 decomposed remains of plants or animals retaining 

 no determinate forms. Future discoveries may in- 

 crease our knowledge of the life of this period 

 preceding the Cambrian, but it is evident that so 

 far as these rocks have been examined, they indicate 

 a great step downward in regard to the variety and 

 complexity of marine life. 



Still we must bear in mind that in later periods 

 there have been times of rapid deposition, in which, 

 in certain localities at least, great thicknesses of 

 rock with few organic remains were formed. We 

 have instances of this in the later Cambrian, in the 

 Ordovician, and still later in the Permian and Trias. 

 Thus in the beds immediately underlying the lowest 

 Cambrian we may be passing through a tract of 

 comparative barrenness to find more fertile ground 

 below. 



It is also to be observed that there is evidence 

 of disturbance occurring in the interval between 

 the lowest Cambrian and the highest pre-Cambrian, 

 which may involve the lapse of much time not 



