Although the number of species in which variation of shape has been investigated is relatively small, due to the broken state of the material, it is possible to outline some new fundamental features of shell morphology.The investigations of Yoldia glaberrima, Leda Westendorpii, Leda pygmaea, and Spisula subtruncata indicate that the length/height ratio of pelecypod valves is very seldom constant throughout the life of the animal. This is important, but some workers are apparently not aware of this principle, to judge by the significance which is often attached to the calculation of means of length/height ratios, or other quantitative expressions of shape. Mean values of this sort have no taxonomic significance unless they are accompanied by information on the size groups of the shells measured.

The exploration activity which resulted in the 31 deep tests reported on in this paper is briefly outlined in the introductory chapter.Mr. F. Ravlin initiated exploration by drilling the two wells at Harte. He held the concession covering all of Denmark from 1935 to 1938, when Gulf Oil Corporation acquired the concession. A large amount of geophysical and geological work was subsequently carried out under the aegis of the Gulf Oil Corporation, and until 1957 eighteen deep tests were completed. Finally, during the period from 1957 to 1959, when the Standard Oil Company of New Jersey was the concessionaire, seismic work was carried out in selected areas, and 11 deep tests were drilled.Among the geological results the most important one was the proof of a well developed Pre-Upper Cretaceous sedimentary basin in Denmark. The rock column includes Pre-Cambrian, Cambrian, Ordovician, Silurian, Permian, Triassic, Jurassic, and Lower Cretaceous formations. A thick evaporite sequence in the Upper Permian Zechstein is the prerequisite of the salt dome province discovered in North Jutland.Oil shows were encountered in dolomites of the Zechstein in South Jutland, but these petroliferous beds proved unproductive. A short blow out of petroleum gas was, moreover, experienced while drilling in the Suldrup salt dome in North Jutland. It is assumed, that a Zechstein dolomite was the reservoir.An abbreviated well log is given for each of the 31 deep tests. Graphic logs of the wells arranged into simple cross sections are found on plates 18 to 22. Bibliographic references regarding fossil species of importance for biostratigraphy are given in the Danish annex at the end of the paper. Most of the species concerned are illustrated on plates 1 to 11.

This is a study of the fossil record of marine Miocene beds in South Jutland, Denmark. The beds have been defined as the Arnum formation and referred to the middle Miocene Hemmoor stage as known in Northwest Germany. The object of the work is to increase knowledge of the Danish Miocene and to contribute data on the development of the North Sea Basin during Miocene time.The introduction deals with the history of Tertiary stratigraphy in Europe and some related problems. Discrepancies and uncertainties regarding the correlation and dating of beds in the separate basins have been particularly emphasized. It is often possible to trace disagreements to the acceptance of unsound fossil evidence. Therefore it is concluded that the lithologic and fossil records of the individual basins should be known in much greater detail before adequate inferences as to the contemporaneity of particular beds can be made. It is also suggested that guide fossils should only be designated when statistically justified.The chapters on the South Jutland Miocene contain an outline of the geo-graphic distribution of the formations, a lithologic description of the water well sections from which the fossil material was derived, and definitions of the Arnum formation (marine) and the underlying Ribe formation (non-marine). The following formations are now recognized in the Miocene sequence of South Jutland:Gram formation: late Miocene Arnum formation and Ribe formation: middle Miocene Klintinghoved formation: early Miocene.The chapters on paleontology consist of a description of the molluscan fauna of the Arnum formation, a discussion of the environmental relationships of recent mollusca, and a section on biostratigraphy and paleobiology.The description of species follows a rigid pattern. The intention being to include as many pertinent facts as possible while using a minimum of technical terms. The variation of shell properties is illustrated by diagrams in a few species, and in some families genetic features have been particularly discussed. The chapter is terminated by a short review and some conclusions regarding the significance of shell morphology.The chapter on environmental relationships of recent mollusca includes discussion of the effects of inanimate environments on shell morphology and the distribution of mollusca. It is maintained that the reaction of recent mollusca to variations in their environment should be known in greater detail in order to provide a sound basis for biostratigraphic conclusions depending on the evidence of fossil mollusca.A discussion of the commonly adopted correlation procedures initiates the chapters dealing with biostratigraphy and paleobiology. It is shown that the "percentage" method by which faunas are correlated on the basis of percentages of species in common should be regarded with much criticism. New correlation formulae, in which are included the total numbers of species in the faunas involved are suggested. It is shown by these formulae and other evidence that the fauna of the Arnum formation in its entirety is apparently in better agreement with the Reinbek and Hemmoor faunas of Germany than with any other fauna of the North Sea Basin.The paleobiological analysis of the fauna of the Arnum formation is based on: the biology of living species; the actual frequencies of the mollusca in the different drilled sections; and the environmental relationships of recent mollusca. It is inferred that a decrease in salinity took place during deposition of the formation. The faunules of the different fossiliferous levels are shown to be derivatives of one community: the Aporrhais alata - Nassa sp.sp. community which inhabited relatively shallow waters of the middle Miocene North Sea Basin.In conclusion some comments are made on the correlation of the well sections as supported by paleobiology. The Nassa cimbrica and N. Fuchsi zones are defined, and the different elevations of correlated levels in the drilled sections are related to structural displacements.

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