Origin of Species Variorum

of another species if we were to examine both ever so closely, unless we likewise possessed many of the intermediate links between their past and present states; and these many links we could hardly ever expect to discover, owing to the imperfection of the geological record. If two or three, or even more linking forms were discovered, they would simply be ranked as so many new species, more especially if found in different geological sub-stages, let their differences be ever so slight. Numerous existing doubtful forms could be named which are probably varieties; but who will pretend that in future ages so many fossil links will be discovered, that naturalists will be able to decide whether or not on the common view these doubtful forms are varieties? ↑ Only a small portion of the world has been geological explored. Only organic beings of certain classes can be preserved in a fossil condition, at least in any great number. Many species when once formed never undergo any further change, but become extinct without leaving modified descendants; and the periods, during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they have retained the same form. It is the dominant and widely ranging species which vary most frequently and vary most, and varieties are often at first local— both causes rendering the discovery of intermediate links in any one formation less likely. Local varieties will not spread into other and distant regions until they are considerably modified and .. improved; and when they do spread, if discovered in a geological formation, they will appear as if suddenly created there, and will be simply classed as new species. Most formations have been intermittent in their accumulation; and their duration has probably been shorter than the average