PLATE I. 



[To accompany Paper R.] 



Fig. 1. A piece of the building stone from the East Side quarry; size> 

 \%xll<2 inches, n. The calcareous bands possessing a light gray color and 

 containing 88.64 per cent, of calcium and magnesium carbonates. 6. The 

 Interrupted siliceous bands, darker colored than the others, rapidly 

 weathering and containing 70.68 per cent, of calcium and magnesium car 

 bonates. 



Fig, 2. The contact between the " blue-greeu-gray " argillaceous 

 material which forms the base of the lower Trenton and the sub crystaline 

 limestone overlying it. A hand specimen 3x4 inches in size. 



Fig 3. The normal building stone layer of the Trenton, — x75. 



Fig. 4. The argillaceous bands which abound in the building stoni 

 layer, a. Calcite in rhombohedral individuals and in granular transparent 

 aggregates, h. The argillaceous matrix, c. Segregated pyrite grains and 

 crystals. 



Fig. 5. The upper part of the magnesian limestone layer just beloAv 

 the St. Peter sandstone, as shown by the borings of the Washburn C Mill, 

 from 204 feet below the surface, — x35. a. The granular limestone, h. 

 (trains of quartz, many of them carrying numerous fluid inclusions. 



P'ig. 6. The upper part of Mr. Swan's layer No. 4, 218 feet below th( 

 surface at the West Hotel, — x35. a. Normal granular dolomitic limestone. 

 h. Grains of quartz, usually rounded. 



