ART. 16. SOME PECULIAR FOSSIL FORMS MANSFIELD S 



As shown in sections 1 and 3, the Miocene bed carrying well pre- 

 served St. Marys fossils occupies the lower 3 or 4 feet of the expo- 

 sures. In section 1 the fossiliferous Pleistocene bed rests uncon- 

 formably upon the Miocene. (PI. 1, A.) The age and the relation- 

 ship of the bed containing both the peculiar spiral and uncoiled 

 forms to the known Miocene are a little uncertain. No exposure was 

 seen at which this bed is in direct contact with the Miocene bed 

 carrying well preserved St. Marys fossils. However,' it appears to 

 correspond to bed No. 2 in section No. 3, a bed carrying entire and 

 fragmental St. Marys shells. There is a possibility that the material 

 composing the bed containing both the peculiar spiral and uncoiled 

 forms has been reworked and that the contained casts of Miocene 

 shells are stratigraphically out of place, the shells being carried in 

 with sediments of Pleistocene age; but the material is finer grained 

 than most of the Pleistocene material overlying the Miocene. 



GBNER,\L STATEMENTS CONCERNING THE PECULIAR FOSSIL SPECIMENS 



In position, the coiled forms stand upright in the deposit, Avhile 

 the uncoiled forms usually are horizontal. The specimens are coiled, 

 nearly straight and branching, or somewhat irregular. The surface 

 of the specimens is usually roughened by rounded or elongated ele- 

 vations. In cross section the tube reveals two distinct parts. The 

 outer or peripheral part is designated, for convenience, the wall, and 

 the inner part, the core. The material composing the core consists 

 of homogeneous, rather compact, fine-grained, ocherous, micaceous, 

 noncalcareous sand. Prints of fossil mollusks were found in the 

 walls of some specimens, but no organic remains were found in the 

 cores. The inner part of the peripheral wall is porous'. 



Coiled specimens. — These specimens are either dextrally or sinis- 

 trally coiled. The upper part (so inferred) of the specimens is 

 more regularly and symmetrically coiled than the lower. The 

 diameter of the whorls of the coil in cross section in some specimens 

 is nearly constant throughout, whereas in other specimens one end is 

 larger than the other. The wall, in cross section, reveals under 

 magnification fine quartz grains cemented by iron oxide. The mate- 

 rial composing the core is similar to that of the wall except that it 

 is less indurated and contains no trace of organic remains. No 

 cellular structure was detected in the thin slides made from the 

 cross sections of the wall. 



Uncoiled specimens. — The uncoiled specimens occur in the same 

 bed with the coiled specimens, but the coiled and uncoiled forms 

 were not found attached, consequently the relationship of the two 

 different forms has not been determined. In general they are stem- 

 like in habit. Some are branching. Usually they are horizontally 

 arranged in the bed. One cylindrical specimen possessing a much 



