The Permian of Mongolia, Vol. 4: A Report on the Permian Fauna of the Jisu Honguer Limestone, of Mongolia and Its Relations to the Permian, of Other Parts of the World (Classic Reprint)

Excerpt from The Permian of Mongolia, Vol. 4: A Report on the Permian Fauna of the Jisu Honguer Limestone, of Mongolia and Its Relations to the Permian, of Other Parts of the World

The fossils described in this volume were obtained during several seasons field work in Mongolia, by the Central Asiatic Expeditions of 1922, 1923 and 1925. They were collected chiefly by Mr. Frederick K. Morris, at Jisu Honguer in southern Mongolia (Latitude 42° 18'N., Longitude 109° 48'E.). The fossils all occur in limestone, much of which is crystalline, varying from coarse to fine-grained. As a rule the fossils are well preserved, but perfect specimens are not easy to extricate because of the nature of the rock, which gives the surface layers of the shell a tendency to become exfoliated. This is especially the case with the larger brachiopods, most markedly so among the Spirifers and Spiriferellas. However, when weathered out, the surface characters are well shown.

Although the strata are strongly disturbed, the fossils in the limestones have suffered almost no distortion. It is only in rare cases that compression and distortion are found.

The geology of this region is discussed at some length by Messrs. Berkey and Morris in Chapter II of this volume, where the character and succession of the several divisions of the series are given. In the field, Berkey and Morris have recognized some twelve successive divisions which have been designated by field numbers. These are given in the list at the end of Chapter II, together with the genus or species most characteristic of them, and by which they will be referred to in the descriptions of Part II.

For the benefit of the general reader, a summary of the entire subject covered in this volume is given in Chapter I.

It has been found desirable to designate the various specimens which were studied in detail, by serial numbers, which are not always, or even generally, consecutive. This has resulted from the fact that the material was described, as its preparation was completed, without reference at the time to the systematic sequence. Often the discovery of additional material, after the original description had been completed, necessitated certain additions, especially in the measurements, and such new specimens have their serial number far removed from those of the specimens previously described.

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