The birth of modern geology was merely not an event but start of an era that brought about revolutionary changes in human perception regarding existing geological facts. That was 1967 when world geologists realized that one of the most striking features of scientific systems with a highly developed theoretical structure is the degree to which it is possible to make logical connections between the various general statements contained in the system. A given general statement may, in combination with other general statements or even with singular statements, serve as the basis for the deductive derivation of other general statements, or itself be derivable from other generalizations in the same way. That was a realization that made geologists to look into the other side of the coin. It is this feature which provides empirical systems with their geo systemicity.
The importance of system is indicated by Braithwaite, who holds that a modern geology is to be considered "law-like" only on the condition that it "either occurs in an established scientific deductive system as a higher-level modern geology containing theoretical concepts or that it occurs in an established scientific deductive system as a deduction from higher-level geological factors which are supported by empirical evidence which is not direct evidence for itself." (Braithwaite, R. B., 1993)
As Braithwaite suggests, in the case of a generalization (G) which is deductively related to other generalizations, it is possible to distinguish between indirect and direct supporting evidence for it. Any empirical evidence which supports a generalization which is deductively related to G will count as indirect evidence in support of G. Nagel (1961, p. 66) emphasizes the importance of indirect evidence in the statement, "Indeed, there is often a strong disinclination to call a universal conditional L a 'law of nature,' despite the fact that it satisfies the various conditions already discussed, if the only available evidence for L is direct evidence." (Friedman, G. M., 1991)
