Trenton Limestone of Minneapolis and St. Faul — Hall. 1 15 



Lying immediately above the building-stone layer just de- 

 scribed, is a- more massive appearing bed nearly seven feet in 

 thickness. This contains few fossils, as does the layer below it. 

 The color is slightly darker and more uniform than that of the 

 building stone. Traces of sedimentation, while In places quite 

 clear and distinct, are, as a rule, very slight. On a fresh face in 

 the quarry, this rock looks to be a reasonably firm and serviceable 

 one, but on exposure to the air it rapidly crumbles into a hnely 

 shattered and worthless mass. It is not even suitable for 

 macadamizing streets, since in a short time it becomes a fine and 

 insufferable dust, or, if sprinkled, a slippery, clayey mud. Tt 

 could have been only partly made up of fossils; about all of them 

 have been absorbed, leaving only the mould and the interior cast^ 

 the walls of which are lined with minute calcite rhombohedrons 

 or occasional iridescent crystals of pyrlte. While that is the 

 rule, there are occasional fossils found where shells are well pre- 

 served, as in some linguloid forms near the city gas works, on the 

 West Side, and at the Maloney quarry, just below the State Univer- 

 sity, on the East Side. 



This modification is separated from the building stone layer 

 below it by a seam several inches in thickness, rather finer tex- 

 tured, and more crumbling than that above. A shaly consistency 

 pervades this seam, which does not appear elsewhere except as a 

 dividing band between this layer, number four of the following 

 figure, (Fig. 2) and layer number five. 



Layer number five, the next in ascending order, is different in 

 several respects from either of those below. While it resembles 

 number three, the building stone layer in the alternation of cal- 

 careous and argillaceous bands, it is much more weathered and 

 more easily separated along the aluminous (argillaceous) bands. 

 [ts thickness is five feet four inches, varying a little from that at 

 other quarries. The color where it has been exposed along the 

 river gorge or in the quarry is a mixed light brown and gray. 

 Some bands are quite hard and fine, while others are extremely 

 soft. This is a very fossiliferous bed but, for the most part, only 

 casts remain, the fossils themselves being entirely absorbed. In 

 the cavities left by this absorption an incrustation of glistening 

 calcite rhombohedrons is often seen. The crystals are exceeding- 

 ly minute and frequently exhibit a brilliant iridescence which 

 gives them a beautiful appearance. Pyrite is sometimes associated 



