On the basis of the results of the multivariate statistical analysis o
f 56 oil shales and shale-like rocks using their 6 essential character
istics these caustobioliths have been subdivided into three classes: l
ipokerogenous shales originating mainly from the lipid. fraction of in
itial organic material and characterized by a high yield of semicoking
oil, kerogen basis, heterokerogenous shales containing organic matter
thoroughly transformed by multi-stage metabolic processes and yieldin
g little oil on low temperature pyrolysis and intermediate shales.