48 



to be mistaken. Occasionally there are beds of dwarfed marine species 

 telling of a brackish sea, and others related to those we find in estuaiies 

 at the present time. You will observe that the remains mentioned are 

 aquatic organisms only, but all these deposits contain, in more or less 

 degree, aerial and terrestrial animals and plants. Many of these fre- 

 quented the seas and lakes, and their remains readily found place in the 

 deposits pertaining thereto, while others have been drowned in lakes 

 or rivers and have been carried out to sea by streams. Some remains 

 of land animals occur in " sub-aerial " deposits, such as blown sand 

 accumulations on the land. 



And, further, we may form a fairly reliable opinion of the climate 

 which obtained during the deposit of these, thus, e.g., the Eocene 

 deposits of Greenland, a country now buried under ice, contain the 

 trees, shrubs and plants of the temperate regions — the Eocene of Western 

 Europe contains remains of cowries, volutes and palms closely related 

 to those found in combination with a mean temperature 30° warmer 

 than at present. 



As has been stated the various formations are characterized (1) by 

 the association of certain fossils, (2) by the predominance of certain 

 families or genera, or (3) by an assemblage of fossil remains representing 

 the life of the period in which the formation was deposited. But the 

 record of the life of the whole series from bottom to top is not an 

 uninterrupted one, and this " imperfection of the Palaeontological 

 Record," as it is termed, is to be regretted, because our knowledge of 

 prehistoric life is almost entirely limited to the palaeontologieal evidence 

 at our disposal. At the outset is what is known as " unrepresented 

 time " or better, perhaps, as " the imperfection of the Geological Record,'' 

 owing to the fact that many missing or undiscovered rock groups are 

 buried beneath others or beneath the waters of the sea out of sight ; 

 that a large portion of the earth, including two great continents, is as 

 yet unexplored ; and also that denudation has played the same havoc 

 with the deposits of bygone ages that it has played with those of today. 



No better example of " unrepresented time " can be had than that 

 oft-quoted break in the strata of Great Britain between the secondary 

 and tertiary epochs. In the upper cretaceous beds there are 500 species 

 of described fossils, and of these only one brachiopod and a few 



