Geology of the lower Amazon region / Charles Schuchert.

  • Charles Schuchert
Date:
[1906]
Catalogue details

Licence: In copyright

Credit: Geology of the lower Amazon region / Charles Schuchert. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    curta. 'Tropidoleptus carinatus is known in a single example from the Oriskanian of Maryland; it is also abundant in the Lower Devonic of Germany, and, as Williams has shown that this shell is also known in the Chemung, it therefore has lost its diagnostic value as a marker of the Hamilton formation. Vitulina pustulosa is thus far in eastern North America a good Hamilton marker, but in South America it is always found in faunas that have an older aspect. This Maecuru fauna has ninety-two species, and of these the following six Oriskanian forms are known in it: (i) Rhipidomella musculosa, (2) Leptosirophia perplana, (3) Anoplia nucleata, (4) Am- phigenia elongata curta, (5) Anoplotheca flabellites, and (6) Tropido- leptus carinatus. Certainly numbers i, 3, and 5 are diagnostic of the Oriskanian, and are usually regarded as guide fossils. Combining these occurrences with the other facts mentioned above, it seems to the writer that there cannot be any doubt that the Maecuru fauna holds the horizon of the North American Oriskanian. If further proof of this is required, the reader is referred to Katzer’s Plates X, XI, XII, and XV. On the other hand, the view of Clarke (who has studied nearly the entire fauna by the specimens), while not exactly that of the writer, is still not widely different (hardly one formation apart). He states (5:91, 92) the following: The opinion expressed by Derby [6; i6g] and Rathbun that the Maecurii and Erere groups bear about the same stratigraphical and paleontological relation to each other as the Upper Helderberg group to the Hamilton, is supported by all evidence now accessible. It is indeed probable that the Maecurd group embraces elements of faunas that elsewhere precede those of the Upper Helderberg (Schoharie grit, Cornif- erous limestone), a fact indicated by the earlier expression of the trilobitic ele- ment and by the presence of certain molluscan species {Platyceras hariti, Anoplia tmcleata) of the same import. Notes on the fauna 0} the Erere formation.—Hartt (2:213) describing the Erer^ locahty states: This fauna has an unmistakable Devonian facies, but it is difficult to deter- mine its exact equivalency. In some features, as for instance in Spirifer pedroana, which closely resembles S. varicosa, the fauna recalls that of the Comiferous, while in the occurrence of Tropidoleptus and Vitulina it approaches the Hamilton. Rathbun (3:260) in his first studies of the Erer6 brachiopods con- cludes :
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