292 GEOLOGY OF EASTERN WISCONSIN. 



stone, and is now called the Lower Buif beds, exclusive of tlie argil- 

 laceous layers at the base,, shows 36.41 per cent, of carbonate of 

 magnesia. A similar analysis of the Lower Blue beds shows 38.39 

 per cent, of carbonate of magnesia. A like analysis of the lower 

 13 feet of the Upper Buff beds gives 43.30 per cent, of magnesic car- 

 bonate, and one of a higher stratum, 34.86 per cent. These analyses 

 were all made from rocks whose exposure to leaching and weathering 

 was as nearly as possible equal, and from adjacent, where not identi- 

 cal, localities, all being from the vicinity of Beloit. 



From these it appears that the quantity of magnesia varies but 

 slightly, and- that the entire amount is large, so that the term dolo- 

 mite is applicable here as well as to the calcareous formations above 

 and below, while the Blue limestone of the Lead region is a true lime- 

 stone, containing but little magnesia. 



In the third place, ths paleontological distinction heretofore 

 drawn does not hold good. The Buff limestone has been regarded as 

 characterized by great numbers of Gasteropoda, Cephalopoda and 

 Lamellibranchiata, especially by species referable to Tellinomya, 

 Cyprioardites and allied genera. But this is at least equally true of 

 the Upper Buff beds of this report. 



The following species catalogued in the report of 1862, as belonging 

 to the Lower Buff limestone, have been found in the Upper Buff beds 

 of this report: 



Cypricardites Niota, C. rotundatus, G. ventricosus, Modiolopsis 

 superha, Tellinomya nasuta, T. ventrioosa, Murchisonia helicteres, 

 Pleurotomaria {Raphistoma) Nasoni^ P. suhconica, Trochonema 

 umbilicatuin, Itapldiitoma lenticularls, Cyrtooeras annulatum,, 0. 

 eugium, Oncoceras Lyons, 0. Pandion and 0. plebium. 



Only one of the list given in the report of 1862 as from the Buff 

 is known to me as occurring exclusively in the Lower Buff, while 

 three have been found in the Upper Buff that have not been observed 

 in the Lower. The majority are common to the two subdivisions, 

 and to this number several allied species have now been added. 

 Cblnmnaria alveolata, also regarded as peculiar to the Lower Buff, is 

 found in the upper beds. 



The strata at Rockton, which belong to the Upper Buff beds, are 

 referred to the Buff limestone of previous authors,^ and a similar par- 

 donable confusion of the two members has undoubtedly been ex- 

 perienced by other writers on the geology of this region. 



These facts are dwelt upon to this extent to demonstrate the ne- 

 cessity for the introduction of a new classification, and of new terms 



' See pp. 89, 90, Vol. V, Geol. Rep. of lU. 



