236 



Repokt of the State Geologist. 



found, wherever examined, to be destitute of fossils and generally of 

 calcareous matter, being a soft, light grey rock, which, when taken from the 

 bed, may be cut with a knife. On exposure it darkens and hardens, losing 

 its plasticity. When soaked in water it becomes a tenacious clay or mud. 

 This condition is probably due to the leaching out of the calcareous matter by 

 the acidulated waters resulting from the oxidation of the iron sulphide, the 

 shale thus losing its most important lithifying element. 



The upper thirty feet or more of these shales are very uniform without 

 any marked dividing layers. There are numerous concretions, arranged in 

 horizontal layers, but, with the exception of the Athyris spiriferoides bed, 

 they are never continuous for any great distance. The Modiomorplia subalata 

 bed, twenty-five feet below the Encrinal limestone, is a continuous stratum of 

 calcareous rock which may be traced for miles, but it never exceeds one or 

 one and one-half inches in thickness, and consequently it is not a prominent 

 feature of the cliffs. The first continuous bed which is sharply marked off 

 lithologically from the shales, lies about thirty-two feet below the Encrinal 

 limestone. This is a calcareo-argillaceous rock, in places a compact limstone, 

 though usually of a more or less shaly character. It is from eight to ten inches 

 thick, and forms a prominent band wherever exposed in the sections. Six feet 

 below it is the first Trilobite bed, of similar lithologic composition and rich 

 in trilobite remains. There are three of these beds separated by layers of shale, 

 all grading more or less into each other, and having a total thickness of some- 

 thing over three feet. Five to seven feet below the base of the lowest trilo- 

 bite layer, are three other calcareous layers. These are the Pleurodictyum 

 h<ds of the succeeding pages. The lowest of these beds, a compact grey argil- 

 laceous limestone of a concretionary character, is again separated under the 

 name of the Nautilus bed, this being the horizon of Nautilus magister, Hall. 



Mar cell us stage. 



Immediately below the Nautilus bed is another continuous calcareo-argil- 

 laceous layer, resembling in lithologic character the Trilobite beds. This bed 

 I have called the Stropltalosia bed, from the great abundance in it of S. truncata. 

 It forms a prominent and easily recognizable band six inches in thickness, and is 

 another convenient reference plane for the beds above and below. Its position 

 is a little less than fifty feet below the base of the Encrinal limestone, and it 

 marks the final disappearance of the Marcellus, and the establishment of the 

 Hamilton faunas.* 



•This Is the bed lettered a on Plate V of the Oebl. of the 4th Dlst. N. Y., 1843, mentioned on pp. 190 and 191 of the text. 



