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Summary A deformation belt runs southwards from Wijdefjorden through the length of central Vestspitsbergen, a distance of over 190 miles. From the stratigraphical summary several factors emerge that are relevant to the structural history. 1. The pre-Downtonian rocks are crystalline schists with a general N.-S. trend resulting from an earlier orogeny. 2. There was a basin of sedimentation in the Billefjorden area in Lower and Middle Carboniferous times. 3. The Carboniferous to Lower Permian succession is concordant in the central portion of this basin. 4. A strip of coarse conglomerates overlying an old fault-line suggests weak faulting activity in Middle Carboniferous times. Fault activity occurred in Upper Devonian times, probably with a strong compressive phase in the earlier part which was followed by weaker gravity faulting 1 near the end of the period. Again in Tertiary times, either gravity faults or flexures formed, depending on the competence of the rocks affected. Parallelism with the trend of the pre-Downtonian metamorphic rocks is striking and renewed dislocations along the Upper Devonian fractures seem to be common. It is concluded that the major Upper Devonian fractures are not gravity faults. Two theories of genesis are possible : firstly, transcurrent faulting with associated upthrust wedges; secondly, high-angle thrusting with a later phase of gravity faulting. The data available appear to favour the second.

From an analysis of data concerning five breccias in the Billefjorden area, Central Vestspitsbergen, and from a consideration of explanations previously advanced of other breccias, it is concluded that the main breccias are due to collapse following solution within the underlying beds.

SynopsisThis paper is the first of a series of reports on the detailed investigations of the Gelogy of Central Vestspitsbergen arising out of the Cambridge Spitsbergen Expedition, 1949. While subsequent publications will consist almost entirely of new data, the purpose of this paper is primarily to compile information obtained previously. Following the Introduction, there is a review of the published literature as it affects the area as a whole; this has been attempted at length to save repetition in the later chapters and in any subsequent papers. The later chapters include a detailed study of the Carboniferous to Lower Permian of Billefjorden, using unpublished material which has been made available from several expeditions of the Scottish Spitsbergen Syndicate, some results from the Cambridge Spitsbergen Expedition, 1938, and from that of 1949 in so far as they affect this particular study. It therefore represents an original contribution resulting from a compilation and checking in the field of the work of a number of geologists.The palæontological results are being worked out separately, but within the area, exposures are sufficient to provide a reliable correlation of the Carboniferous to Lower Permian succession recorded in a number of vertical sections. We have found that the very variable facies can best be grouped into the following formations, retaining so far as possible the earlier names:The major Devonian diastrophism was followed by erosion, deposition, and again erosion in the Devonian. Culm of estuarine facies was then deposited in a basin due to subsequent movements along a great north-south Devonian fault-belt. They rest on the Devonian to the west of the fault-belt and on pre-Devonian to the east. After the Culm, local conglomerates reflect movements along this fault-belt at the western margin, and in the centre of the basin evaporites are developed. Although a number of disconformities can be traced, there is no important unconformity in the basin. The widespread transgressions recorded outside this area, equivalent to the base of the Cyathophyllum Limestones and again to that of the Brachiopod Cherts, are marked within the area by distinct change of facies but no angular relationship of the bedding.The distribution of these various formations is shown in a geological map to a scale of 1:100,000, which is the first comprehensive topographical and geological map of the whole area to be published.

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