THE CAMBRIAN PERIOD 



493 



the deformation that closed the Proterozoic, or to the opening 

 stages of the Paleozoic, previous to the demonstrated Cambrian. 

 The profound climatic significance of these glacial formations is 



Fig. 370. Section showing glacial beds, South Australia. 



obvious. The testimony of Cambrian fossils, on the other hand, 

 implies nearly uniform climatic conditions throughout all regions 

 where fossils have been found, and the wide spread of the sea 



Fig. 371. A glaciated bowlder from the Cambrian till of Petersburg, South 

 Australia. (Howchin.) 



during the later part of the period would seem to point to oceanic, 

 rather than continental climates at that time. 



Duration of the Cambrian Period 



There is no way of making a reliable estimate of the duration 

 of the Cambrian period. The destruction and the removal to the 

 sea of such large volumes of rock as are represented by the sediments 

 of the Cambrian required a very long period of time ; but since there 

 is no standard rate at which any sort of sediment is known to 



