42 HYATT ON THE TERTIARY SrECIES 



Fraas and Quenstedt both attribute the formation of the circular valley and the 

 superficial aspect of the Cloister Ridge largely to denudation, and I think the inference 

 is very well founded that a considerable proportion of this must have taken place before 

 the formation of the lower strata of the Pits. These partially consist in the lower 

 part of the Little Pit of a peculiar coarse sand, containing fragments of rock, 

 both resembling in color and texture the Cloister Ridge rocks, though in the small number 

 of fragments examined no fossils were found. The dark, reddish-brown color of the sand 

 in the lower strata of the Pits predominates, whereas, in the upper parts above e and 

 /, this is not the case, and pm-e white shell sand is more abundant. Above these 

 again comes in some of the sections a sort of rubble, like that of the basal strata, 

 containing Lymnea again in abundance, whereas, in the intermediate deposits, it was 

 l:)ut sparsely repi'esented. I was under the impression when at Steinheim, that the 

 Cloister Ridge rocks were considered older than the Pit Deposits, but nevertheless 

 spent a ccnisiderable portion of time in studying the relations of the two, and made 

 a series of observations, in order to find out their relations to each other, knowing 

 that but little attention had been paid to this part of the field. 



Dr. liilgendorf, in reply to my questions, wrote me on the 13th of November, 1877, that in 

 the Old Pit the massive Fresh-water Limestone of his Section 2 ^ was surely a tufa similar 

 to the Cloister Ridge rocks. " ' Der massige Siisswasserkalkstein ' welcher die Grundlage 

 des Profils M 2 bildet (p. 481) ist sicher ein Tuff gewesen whnlich den Felsen, die den 

 Klosterberg kronen." He also states that he found in one of his excavations a block of 

 '' Tenuis Tuft'a." resting upon the Jura, which was four and one-half metres thick, and adds 

 that .they (the Cloister Ridge rocks) agree with the older layers of the pits.. The view that 

 the C'loister Ridge rocks and the lower Pit Deposits were fonned at the same time is 

 rendered improbable by all the facts stated above ; by the composition of the lower Pit 

 Deposits ; by the difference in the structure of the rocks, which show that conditions 

 existed which made the lake at this period very different, a reservoir of lime-laden water 

 unfavorable, either from this or some accompanying cause, to the existence of such vast 

 numbers of shells as appeared in the purer Avaters of the Pit Period ; by no signs of 

 transition between the two, and by the position and inclination of the strata of the Pits, 

 which dip away from the unstratified Cloister Ridge rocks, indicating a want of conform- 

 ability, which, however, could not be proved because no contacts were exposed. 



The influences which effected the deposition of the Cloister Ridge rocks, were indepen- 

 dent of any periodical changes which could so materially alter the ((uantity of sediment held 

 in suspension by the water at any season of the year as to produce regular strata of slight 

 thickness. Whereas, within a few feet occur the Pit Deposits regulai'ly stratified in such a 

 way that we can say \^th certainty that there were periods of quiet waters for the lime- 

 stones and clays, and periods alternating with these during which much coarse sediments 

 were transported and deposited in the form of sands and rubble, etc. 



I am aware that the deposits of water impregnated by mineral springs, may take j)lace 

 in very narrow and confined areas, but that such a thickness of rock exceeding that of the 

 Pit Deposits, would have been deposited on the Cloister Ridge in the immediate vicinity of 

 the Pit Deposits, in tlie middle of a lake, and yet lieen wanting in the larger number of 



1 See p. 44 of this Memoir. 



