OF PLANORBIS AT STEINHEIM. 53 



cc 1 of Sect. 3, and Section 10 above, and of Sect. 6, is not the same as formation x 2 

 of Sect. 7, since they are separated by the clay bed m, and for the same reason formation 

 X 3, -of Sections 3 and 7, is not the same as x 2, since these are separated by formations n 

 and o. There are really, therefore, three series of formation x, due to the colonization 

 and re-colonization of the same spots by the persistent forms of PI. discoideus and 

 PI. irochiformis. How is it possible for x bed fauna to alternate in this way with 

 clay in pockets, or in folds, as the case may be, or with beds of pure shell-sand and 

 shell, without recognizing their resemblance to the same mode of occurrence of similar 

 pockets in many of the clay layers below ? That they were ruins of the older 

 irochiformis formations and were swept into these well defined local depressions is 

 of course possible, but it is an assumption which an experienced collector would be 

 slow to adopt. It is a well-known fact that deep holes in water-ways are usually 

 more or less filled with dead shells of various kinds, but these usually exhibit decisive 

 marks of the rough handling they have received from the currents. 



This does not appear in the shells of the x beds so far as I have observed them, and 

 even in such a small lake as Steinheim this must, I think, be asked for. Many shells are 

 unquestionably water-worn and, if so, why not all in these beds if, as claimed by Dr. 

 Hilgendorf, they are made up of wholly transported materials. 



The upper layer of limestone in the Old Pit, and all the layers of limestone above 

 formation I, in the East Pit are fragmentary. These fragments lie more or less closely 

 together, and look very much like continuous layers broken up in place by the bending 

 of the strata. Whether these may be taken as evidence that the strata lying upon them 

 at the time of their last elevation was not of great thickness, it would be hazardous at 

 present to say. One fact, however, seems to indicate something of this sort. The lime- 

 stone above Z, was probably free from any great pressure at the time the folds took place, 

 which formed the pocket at a; I, in section 10, as also was that of I in the Old Pit. This 

 suggests that the same condition of afEairs probably occasioned the breaking up of the 

 succeeding layers in the East Pit. 



The formations seemed to have been disturbed in the East Pit, and in the Old Pit, at 

 about the same time, that is after the deposition of x 1 upon I, or k, I. This did not seem 

 to affect the strata in the New Pit, however, until after the deposition of clay beds con- 

 taining fossils, which caused me to synchronize them with m and n, o, in the East Pit, and 

 the bed x 2 which was deposited between them. 



The broken aspect of the layers of limestones were not, when 1 saw them, similar 

 to the descriptions given by Dr. Hilgendorf in " Neue Forschung in Steinheim," p. 452, 

 but possessed in all the cases observed by me, a regularity which I could only 

 account for as the result of the bending of the strata after deposition. It is well known 

 in this country that not very dissimilar effects occur from the compression of gneiss 

 occasioned simply by the removal of the superincumbent rocks. The upper layer 

 relieved from the weight, in some spots forms miniature anticlinals and synclinals, and in 

 others bursts with considerable violence in the quarries of Monson, Mass., where these 

 phenomena have been observed by Prof. W. H. Niles.^ I could not understand the reg- 



1 Pi-oc. Bost. Soc. Nat. History, xiv, 80. 



