The sum of the geochemical cycle of each element should have an average equal to its primary value. Therefore, it should be possible to obtain an isotopic balance for eache lementin the crust. The parameters involved are: the concentration of these elements in the igneous, sedimentary and marine divisions of the crust, the amounts of each environment, and the isotopic cornposition of these elements in it. Hence, isotope ratio data provide. an independent method of estimating the quantities of the imnportant divisions of the crust. From this standpoint, we can estimate the mean average value of the crust and the mantle. The abundance data herein are restricted to the lithosphere, marine hydrosphere, and the cosmosphere exclusive of tektite. The individual contributions to the abundance data from other divisions, such as the hydrothermal ore deposits, the biosphere, the atmosphere etc., are negligible. One general feature of the geochernical cycles of boron and lithium isotopes is discussed by comparing them to the sulfur isotope cycle. The mean values of their abundances and their isotope abundance ratios in the crust were assumed to be roughly 12.7g/ton(B), 20.0g/ton(Li), and 4.07(B
11/B
10), 12.5(Li
7/Li
6).
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