CARBONIFEROUS LIMESTONE. .113 



/aces in the same manner as if they were the fissure plains of a 

 crystal or of innumerable parallel crystals ; its chemical composi- 

 tion is 69 per cent of quartz with 30 per cent carbonate of lime. 

 Upward in the series the arenaceous beds are gradually replaced 

 by pure limestones, but thin seams of quartz sand are yet occa-' 

 sionally wedged in between the calcareous layers. Not unfrequent- 

 ly the strata of this horizon are in brecciated condition ; locally 

 they are found to be very fossiliferous — numerous Fish-teeth 

 (Helodus, Cladodus, etc.), Productus Flemmingii, Bellerophon sub- 

 Isevis, Zaphrentis spinulosa, Fenestella, Polypora, and Trematopora 

 being the forms noticed. The next higher strata are pure, light- 

 colored limestones with smooth, conchoidal fracture, in beds of varir 

 able thickness, interlaminated with concretionary seams of Horn- 

 stone ; fossils are generally not very abundant, but certain seams 

 are crowded with them over widely extended surfaces. The stems 

 of Lithostrotion proliferum, also Syringopora ramulosa, Allorisma 

 clavata, and various Bryozoa, are not uncommon. The numerous 

 quarries of Bellevue are opened in these beds, which reach 8 or lO 

 feet in thickness. Their chemical composition is : 



Carbonate of lime 96 



'' magnesia i .0 



Hydrate of iron oxide 0.5 



Insoluble residue 1.5 



In the quarries, we observe above these limestones a stratum of 

 a brown ferruginous dolomite with dull, earthy fracture, and about 

 2 feet in thickness, and following next to it about 3 or 4 feet 

 of light-colored limestones identical in appearance with the beds 

 below. Higher still is another belt of brown, ferruginous dolomite 

 rock, about one foot in thickness, and either in continuous layers 

 wedging out at both ends, or in seams of irregularly-shaped sep- 

 taria surrounded by calcareous shale. A few feet of light-colored, 

 thin-bedded lime rock deposited on top of the brown concretionary 

 seam are the highest strata noticed. 



The brown dolomite rock is composed of 



Carbonate of lime 56 



" magnesia 23 



Iron oxide hydrate, with some alumina 5.5 



Silicious residue 9.0 



