87 



5. Bluish clayey marl with much green sand, containing the 



same fossils as No. 4. It washes or caves out from 



under No. 4, which overhangs it 4 to 5 



6. Massive joint clay, yellow on exposed surface, blue when 



freshly broken; no fossils observed. Extends below the 



water level to unknown depth; exposed 3 to 4 



The rock of this formation, which seems to be the best suited 

 for cement material, is the soft "chimney rock" or orbitoidal 

 limestone of bed No. 3 above. This usually quarried for chim- 

 neys and other constructions by sawing it out and dressing it 

 doAvn with a plane into blocks of suitable size, which are then 

 laid like brick. 



The numerous analyses given below will show that this rock 

 is a purer limestone than most of the material of the Selma 

 chalk of the Cretaceous formation above considered. In ce- 

 ment making it will, in consequence, require a larger proportion 

 of clay to be mixed with it, and! the question of obtaining suit- 

 able clay in sufficient quantity and in close proximity becomes 

 one of some importance. The residual clay left after decompo- 

 sition and leaching of the limestone seems to be fairly well 

 adapted to the purpose. Besides this residual clay some analy- 

 ses have been made of the clays of thie river and creek bottoms 

 of the country near the limestone outcrops, and of the clays of 

 the Grand Gulf formation, which very generally in this section 

 overlies the limestone. Some analyses of the last named clays 

 have been made from material occurring near St. Stephens, and 

 near Manistee Junction en the Repton Branch of the Louisville 

 and Nashville Railroad. At this last-named locality the clay 

 is present in sufficient quantity to be oi value if the composition 

 is suitable. 



Details of Localities. 



St. Stephens. The first locality to be considered is the bluff 

 at St. Stephens, a section of which has been given, andl it may 

 be taken as a typical section of the formation everywhere. At 

 St. Stephens the whole of the soft orbitiordal limestone or 

 "chimney rock" might be used, as the composition is uniform 

 throughout. The overlying harder limestone has almost the 

 same composition, but it is less easily crushed and handled. It 

 may be quarried here from the surface down, as it is covered 

 only by a thin layer of residual clay. The characters of the 

 limestone and of the clay from here are sufficiently well shown 



