68 



STRATA. 



''GROUP— (Era). 

 I. Archizoic. 



II. Palaeozoic. 



III. Mesozoic. 



IV. Cainozoic. 



V. Anthropozoic. 



S YS TEM— (Period). 



Cambrian. 



Ordovician. 



Silurian. 



Devonian. 



Carboniferous. 



Permian. 



Triassic. 

 Jurassic. 

 Cretaceous. 



Eocene. 



Miocene. 



Pliocene. 



Pleistocene. 

 Recent. 



Approxitnate 

 thickness of Strata. 



70,000 feet. 



42,000 feet. 



15,000 feet. 



3000 feet. 

 600 feet. 



This enormous thickness of about 130,000 feet represents 

 a vast duration of time and we can only compare one part 

 with another. 



It has been estimated that at the present time the average 

 rate of deposition may be taken as about i foot in 1500 

 years. This would give us about 200,000,000 years, which 

 with corresponding periods of elevation might be 400,000,000 

 years. Such a calculation is really of practically no value as 

 there are many factors which might easily multiply the 

 figures. 



The Archizoic group have strata in many cases modified 

 by heat and pressure and they are probably by no means 

 the first strata. In other words, the origin of animals is 

 antecedent to the Archizoic Era. Thus, the strata of this 

 era show Arthropoda, Echinodermata^ Mollusca and other 

 phyla, all sharply differentiated as at the present day. 



The geological record does not, therefore, help very 

 much in giving us the original ancestors of these phyla, but 

 it forms a very important guide with regard to the higher 

 animals. Thus, although fishes are found in the Silurian 

 system the other five orders of Vertebrata only occur there- 

 after. Hence there is always hope that the geological record 

 may assist us in tracing the descent of the higher vertebrate 



This table is taken from HLEckel's " History of Creation." 



