The sulphur isotope abundances in the free asphalts, asphalts extracted from the supposed source rocks, and the inorganic sulphur compounds of the source rocks of the Uinta basin have been defermined. The results show that both the asphalts and inorganic sulphur compounds become more and more enriched in S³⁴ with decreasing age and decreasing depth of the deposits, the youngest sediments being enriched 31 ^pmil as compared with 20 ^pmil for sea water sulphate. This one-to-one correspondence between S³⁴/S³² ratio and age and depth of deposits is, in view of the changes in the nature of controlling environment which occurred, strong evidence in favor of a biological theory of S³⁴ enrichment in inland lakes and seas.

The free asphalt and asphalt extracted from the source rocks were found to have almost identical sulphur isotope ratios in the case of wurtzilite and albertite. However, in the case of the ozocerite, the asphalt extracted from the supposed source rock has quite a different S³⁴/S³² ratio from that of free asphalt. These results confirm previously suggested relations except in the case of the ozocerite.