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The lithologic and paleontologic aspects of the Silurian rocks in North America have been analyzed. The faunal study has resulted in recognition that, at least as far as the Northern Hemisphere is concerned, the Silurian faunas are relatively cosmopolitan. This fact permitted use of the British shelly fossil Series and Llandovery Stages and Llandovery through Ludlow graptolite Zones for correlation. The stratigraphic succession of brachiopods in North America has led to the elucidation of several phyletic lineages. These and the time-stratigraphic units have been utilized in constructing a correlation chart of the North American Silurian rocks.

Analysis of the distribution of the North American Silurian rocks, their faunas, and their compositional and textural aspects has revealed certain broad patterns. Dolomites are found over the continental interior. They are rimmed by limestones. The limestones grade outward into fine-grained terrigenous deposits which grade, in turn, to coarser-grained terrigenous materials. The consideration of these broad patterns of rock type distribution has led to the conclusion that the continental interior was covered during much of Silurian time by marine waters. This conclusion poses the problem of finding sources for the terrigenous debris of the same age which rims the vast expanse of carbonates. Satisfactory sources for much of this debris have not been recognized but are inferred to be potentially present around the continental margins.

The broad expanse of Early Paleozoic carbonates covering much of the continental interior suggests that later areas of geo-synclinal deposition and orogenic activity situated upon the carbonates were controlled by differential vertical movements.

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