Trenton Limestone of Mhinea/polis and St. Paul — Hall. 12J^ 



this Academy, and were described in 1882 by Professor N. H. 



Wincheil.* 



But the especial point to which attention is now to be called 



is the character of the upper part of the magnesian limestone im- 

 mediately underlying the St. Peter sandstone, the layer numbered 

 4 above in Mr. Swan's West Hotel record and numbered 16 in 

 Mr. Whelpley's record as published by Professor Wincheil. 



Mr. Swan, at the time he reached this layer, handed the 

 writer some chips from the borings, remarking that he had been 

 told to watch for a quartzite layer. 



The chips proved the rock to be nothing more than a l^yer of 

 limestone, probably dolomitic, with grains of quartz sand inter- 

 mingled. In the upper part of the layer the color was of a brown- 

 ish red, due to the presence of ferric oxide, distributed somewhat 

 irregularly through the stone . This irregularity consisted in the 

 intenser staining of scattered spherical masses of rather minute 

 size, giving the stone the a])pearance of a dolomitic clastic rock 

 scattered through which are numerous grains of quartz. These 

 grains are usually small but there is occasionally one of considera- 

 ble size. 



Figure 6, Plate I, shows a section of one of the chips fur- 

 nished by Mr. Swan. Several of the grains of quartz can be seen 

 but the rounded reddish areas mentioned do not well appear in the 

 figure. The material effervesces and rapidly disintegrates in 

 liydrochloric acid, leaving the quartz grains behind as an insoluble 

 residue. 



This lithologic condition of the borings led the writer to look 

 over the borings of the Washburn '^C" artesian well, a series of 

 which belongs to the general museum of the University of Min- 

 nesota. In the description of thes« borings already referred to, the 

 layer in which the boring ceased was pronounced a ({uartzite, like 

 hat at Baraboo, Wisconsin.! But when a piece from these bor- 

 ings is placed in hydrochloric acid, it effervesces rapidly and breaks 



*Tenth annual report, Gool. and Nat. Hist, survov of Minnesota, 1881. 

 l)p. 211-215. 



fTlH'. des(:ri])ti(>n is as follows: ''No. 16, which is the nnl limestone, so 

 called, of the East Minneapolis well, Jias not any of the (lualities of a lime- 

 stone. It is a coarse red i^ritstone, or arenaceous lelsite, the ^irains beinj? 

 pure white silica, and the cement itself an amorphous red feldspathic sub 

 stance, seen to result in many (tases from incipient metamorphism of the 

 shales of the formation, disturbed by ii«:ne()us eruptious, at Lake Superior. 

 In other words, it is a layer of the red quartzite formation seen at New 

 Ulm. and at Baraboo, Wisconsin. The East Minneapolis well found this 

 layer to be lb2 feet thick, * * *" Loc. cit. pp. 2i:J. 214. That is a moat 



