514 (JEOLOGT OF OHIO. 



thoceras, Pleurotomaria, and Syringopora. The stratum exposed here, I 

 think, is the same as No. 4, at Gard's quarries. 



Another exposure on the land of A. Dickey, near Weaver's Station, 

 south-east quarter, section 29, Neave township, shows only the surface of 

 the Niagara limestone, it forming the bed of Mud Creek for 150 yards or 

 more. So near as can be judged, the rocks here, as elsewhere, are hori- 

 zontal, but differ slightly from the three exposures above in other respects. 

 They are distinctly laminated, breaking out in thin but irregular flags ; 

 very sandy in texture, and mostly of the ordinary buff color, but in 

 patches here and there have all the appearance of a red sandstone. The 

 light colored portions, I understand from a very imperfeot experiment 

 performed there some years ago, produce a fine white quality of lime, but 

 the other resembling red sandstone becomes very hard when subject to 

 heat. This fact, I think, is attributable to imperfect burning. This rock 

 was employed in the foundation of a mill which stands near by, but it is 

 evidently too soft for building purposes. The utter absence of fossils or 

 traces of any, is to be noted as a very peculiar feature compared with the 

 Guelph beds in other portions of the county. 



The only other exposure of the Guelph rocks occurs on the lands of 

 C. C. Walker, near New Madison, north-weat quarter, section 24, Harrison 

 township, where it was formerly quarried and burned for lime by C. B. 

 Northrop, but has now been abandoned. A much worn section of six or 

 eight feet is still visible, showing the same general features of this 

 formation as displayed elsewhere. 



It is impossible, from the meagre sections afforded, to give the exact 

 measure of the thickness of this formation in Darke county. Prof. Orton 

 gives to this phase of the Niagara rock at Hillsboro, Ohio, twenty feet, 

 and at Springfield, where it probably reaches its maximum, forty-two 

 feet. Twenty or thirty feet, however, might be considered a safe esti- 

 mate here. 



The fossil contents constitute a far more interesting feature of the 

 Guelph beds than any yet described. The life here indicates somewhat 

 different conditions from those shown by the division elsewhere. 



First might be noticed the rarity of Pentamerus oblongus, but four or five 

 specimens having ever been found. Its place, however, as to abundance 

 and otherwise, is fully supplied by another species of the same genera, 

 P. pergibbosus. Lower down in this formation, both at Covington, Miami 

 county, and New Paris, Preble county, the P. oblongus constitutes a good 

 part of the rock. All fossils here, it must be remembered, are repre- 

 sented by casts; and though the rock weathers very rapidly, the casts, 

 when newly exposed, are for the most part very beautiful and perfect. 



