Trenton Limestone of Minneapolis and St. Paul — Hall. 121 



I. The buildinc: stone layer: the rock analyzed as a whole. Professor 

 Dodge. 



II. The building stone layer: the clean calcareous portions with tlie 

 dark alumino-silicious bands carefully removed. See Plate. I, Fig. 1 a. Pro- 

 fessor Dodge. 



III. The building stone layer: the dark alumino-silicious bands with 

 the calcareous portions removed. See Plate I, Fig. 1 b. Dr. W. A. Noyes. 



IV. The layer directly above the building stone layer: the one which 

 crumbles badly on exposure to the air. Figure 3, layer 4. Horace V. Win- 

 chell. 



Several other analyses of this limestone have been made in 

 the chemical laboratory of the University by Professor Peckham, 

 Professor Dodge, Mr. Sidener and the students, but the exact 

 stratigraphic position of the material is not known. 



In the preceding description of the microscopic characters of 

 the several layers pyrite was mentioned as occurring in all portions 

 of the formation but particularly in layer numbered four in figure 

 two (p. 117). In the building stone layer only occasional segrega- 

 tions of this mineral were seen and it is quite likely that what 

 iron appears in the analyses is in the form of an oxide as Professor 

 Dodge and Dr. Noyes have reported. In the layer above that the 

 presence of pyrite in hand specimens and in their sections is so 

 constant the absence of sulphur in the analysis reported was a 

 matter of surprise.* 



The Ecoj^omic Aspects of the Trenton. — For lime this rock 

 seems to be entirely unsuited. The miscellaneous mixture of ma- 

 terials which the analyses disclose prevents the formation of a firm 

 binding material by the process of calcining. Although silica and 

 almuina are both present, the rock in all its layers is unfit for 

 hydraulic cement. 



For economic purposes, the upper layer, number five of Fig. 2, 

 (p. II 7)is used in places as a sort of rubble, and the best portions of 

 number four can be used when the work is to remain underground, 

 and a perpetual dampness is insured. The building stone layer has 

 the best set of qualities. Where the stone from this layer is 

 placed i)i horizontal position, its strength and durability are both 

 very good; but the whole formation is far from beautiful, and is 

 rapidly going out of use, save in certain kinds of foundation work. 

 The peculiar effects of weathering which this stone exhibits, and 

 *!Subsequently a partial analysis was made by Mr. A. 1). Meeds, who 

 determined nearly two per cent, of sulphuric acid present in a portion of 

 the pnnif siip])ly of material from wliicli the foregoinir analyssis was mad«\ 



