CATSKILL GROUP. 187 



The structure which the hard grey sandstone often presents, is also highly characteristic 

 of it. It appears in many localities, generally forming the surface rock, usually in layers 

 from four to ten feet thick, and nearly horizontal in position. Each of these layers is subdi- 

 vided into numerous parts, from one to more inches thick, often disposed in oblique divisions ; 

 the surface of some straight, others bent; the divisions usually overlapping each other, 

 showing considerable symmetry, presenting altogether a singular conformation, and a highly 

 picturesque rock. Where this rock has not been exposed for a long time to the weather, the 

 structure is not so obvious as in those masses which for ages have been subjected to it ; the 

 latter exhibiting it fully. 



The cause of this peculiar angular arrangement is not yet satisfactorily determined. That 

 it is not connected with stratification is obvious from the disposition of the whole or larger 

 masses, being in horizontal layers, as they may be termed, so usual with those of the New- 

 York system in the district. Among the many localities where this structure exists in the 

 most marked manner, is one in the road from South Norwich to North New-Berlin, near 

 Matherson's pond ; one on the hill-side, near the top, below Oneonta ; on the west side of the 

 Chenango, above the village of Greene ; on the Genegansette, above the same village, etc. etc. 



S3. 



The above wood-cut will give a good idea of the appearance of this rock ; the upper part 

 showing all the regularity of a pile of boards, to which it has been compared, and the lower 

 part the oblique lines of division which so commonly accompany it. The engraving is from a 

 drawing made by Mr. Mason of Philadelphia, from the same group of rocks in Pennsylvania, 

 and is giveh as a substitute, not having a specimen of our own ; which is to be regretted, so 

 finely is the peculiar structure of this rock exposed near Matherson's pond. 



Between the Catskill and the Chemung groups, no hne of demarkation was observed in 

 either State. In ascending upwards from the Chemung group, the fiirst signs of change which 

 usually appeared was a diminution, then a disappearance of the fossils of the Chemung, a 



