OF PLANORBIS AT STEINHEIM. 87 



was largely mixed with clay. The strata a2 and aS, in Section 5, both contain the 

 typical forms of stratum al, but not quite so fully represented in a2 as in al, or in aS, 

 as in a2. They seem, therefore, to be diminishing at the end of this period, in this 

 part of the lake. The deposits of a2 are distinct from al ; they consist of masses and 

 granules which resemble in character the adjacent porous limestone, or the older rocks 

 described previously as forming the mass of the Cloister-ridge. Without the contained fos- 

 sUs it would not have been possible to have synchronized the two formations, namely, the 

 single stratum at the base of Section 6, and the three strata at the base of Section 5. The 

 fossils, however, include a similar association of forms. PI. Steinheimensis, PL tenuis and 

 PI. discoideus are abundant, and PL trochiformis is comparatively rare. 



Formation " b," Old Pit. 



This contains no fossils, but was situated immediately under Formation e, in both 

 of the holes dug in the Old Pit. It contained shell-sand, and a considerable proportion 

 of clay, in Section 6, and was almost wholly of clay in Section 5. 



Formation " c," Old Pit. 



This consisted, in the first hole dug, of 250 mm. of clay, in layers, and 250 mm. 

 of limestone layers, all more or less filled with fish remains ; in Section 5, however, in the 

 second hole, the limestone occurred in layers regularly divided thoughout by layers 

 of clay. No shells were found associated with the fish fossils. The general distribution 

 of this Formation and its peculiar fossils makes it very valuable as a fixed level, 

 from which to estimate the relationship of other formations. 



Formation " d," Old Pit. 



This consisted, in the locality first explored in the Old Pit, of clay and sand mixed, 

 300 mm. in thickness, and in the second place. Section 5, of sand exclusively, the 

 thickness being approximately 270 mm. The fossils were scarce and difficult to 

 gather, because this formation formed the floor of the Pit in both sections. 



The following fossils were obtained : 

 PL discoideus. PL trochiformis. PL minutus. 



They are figured on pi. 2, line b, figs. 5-16. 



Formation " e," Old Pit. 



This consists of shell-sand 1 m. in thickness, and abundance of fossils, especially 

 of the smaller forms. The color differs somewhat from this ordinary shell sand, and 

 it appears of darker or brown color, as if made up of the debris of darker limestones 

 on the hiU. 



The following fossils were obtained : 



T,- -,. . 7 TJ7 denudatus P7 costatus 



PL discoideus. JT t. minnms ■ ■'■ '' minutus- 



PL trochiformis. PL denudatus. PL ""'S^- 



PL minutus. PI- costatus. PL tenuis, var. Kraussii. 



They are figured pi. 2, lines c, d, and e, figs. 1-17. 



