While the first scientific theories on the origin of petroleum (Berthelot in 1866; Mendelejeff in 1877) were based on non-biogenic processes, an increasing evidence in favour of the biogenic theory has been accumulated, thanks to the combined contribution of geologists and gewhemists. It is fair to say that the views of the great majority of scientists throughout the world concur on this basic point of biogenesis.
All authors of the six officiai papers presented agree on the biogenetic theory of petroleum origin, and several papers have discussed in detail the questions of the starting organic material, of the processes by which the parent material is gradually converted into petroleum, and the factors, such as time, temperature and catalysis, which play a role in this transformation. The paper presented by Prof. A. A. KARTSEV, for example, defined a principal phase, or stage, in the formation of petroleum from the parent organic material. In this connection, Prof. S. P. MAXIMOV reported some interesting new results carried out at VNIGNI (Moscow), using also carbon isotopic analysis, whereby it has been possible to reconstruct the various phases of the generation of oil and gas, assigning time values to each of them in specific sedimentary basins of the Soviet Union. Work of this kind can, indeed, be of great value in evaluating the possible petroleum reserves in given areas.
Still on the matter of the "principal" stage of oil formation, developed originally by Prof. N. B.
VASSOEVICH, an important contribution to the discussion has been given by A. M. AKRAMKHO- JAEV (Academy of Sciences of Uzbiekistan Soviet Socialist Republic), who reported the results of a systematic study on the organic matter in sedimentary rocks. Primary, autochtonous organic material was determined separately from the allochtonous one. The composition of the syngenetic organic materials was compared with that of petroleum in the reservoirs of the same basin, to establish a genetic relationship; furthermore, it was found that the concentration of residual syngenetic bitumoid organic matter is related with the paleo-depth profile of the source rock. When the rock has been buried to a maximum depth greater than 4000 m, a drop in the concentration of autochtonous bitumen was noticed, which is explained on the basis of the progress of the naphthogenetic process, in agreement with the theory of petroleum formation zonality proposed by Vassoevich, Sokolov, and by other Soviet scientists.
The paper by Prof. MIRCHINK et al., presented by Prof. V. A. SOKOLOV, reported the results of experimental studies, with laboratory models, simula
