MEDINA SANDSTONE. 73 



It is again seen at Squire Parks' mill dam, to the east of Amboy centre, with some small 

 accretions of shale which look like rounded fragments ; these, by decomposition and removal, 

 produce cavities in the sandstone. Yellow spots of hydrate of iron are also observable upon 

 the sandstone. 



At Petrick's mill, half a mile to the east of Colosse, the red sandstone appears in the bottom 

 of the creek under the bridge. It is of the harder variety ; and like all the sandstone of this 

 mass in the district, it appears to resist the destructive action of atmospheric agents much 

 better than the same mass in the fourth district, being less mixed with argillaceous materials. 

 Loose, masses or fragments of the sandstone are very abundant around the village, being used 

 for field enclosures. 



On the same creek, about four miles below, it forms the low fall at Mexicoville, being one 

 of its extreme north points. About three sand layers are there exposed, with some streaks of 

 grey, the layers about fourteen or more inches thick. From the small exposure here and in 

 most other places, the dip of the rock was difficult to determine, appearing to be horizontal. 



The greatest exposition of the red sandstone in Oswego county is at Fulton, on both sides 

 of Oswego river, forming the banks and the falls. The upper layers are covered with Fucoides 

 harlanii, some in admirable preservation and of gigantic dimensions, intermixed with the smaller 

 and more common variety. In some of their parts the fucoids have been replaced by small 

 pebbles, showing a peculiar organization and material which could admit of such replacement, 

 the form being well preserved. 



The upper layer of the falls is a hard, light-colored, variegated red sandstone ; the next below 

 it, is a mixture of sandstone and slate, more or less friable, and of a dark red color ; the third, 

 a red and grey sandstone, and of intermediate shades, which is quarried for buildings, hearth 

 stones, etc. ; and a fourth, same as the third, with the color more general. Each of these 

 layers is about two feet thick. 



The sandstone is seen for half a mile below the falls, by the side of the canal path. A 

 considerable part shows the water lines of deposition, being formed of wedge-shaped masses 

 of unequal dimensions as to length, and either curved or straight. These are again subdivided, 

 the parts being disposed at various angles to each other, and generally arranged between pa- 

 rallel lines, conformably with the other layers with which they are associated, the whole being 

 nearly horizontal. Along the bank this structure extends to two or three layers, but at the 

 falls it is confined to the one below the upper rock. 



These oblique lines of structure are seen to greater advantage in the red sandstone of the 

 Clinton group in Herkimer county, and are highly characteristic of the grey sandstone of the 

 Catskill group as it appears in Otsego, Chenango and Broome counties. It is the common 

 structure of the roofing slate of the Hudson group, and is also seen in a hill of sand through 

 which the Camden and Amboy railroad in New Jersey passes. 



Three causes present themselves in explanation of this structure ; 1, oblique depositions by 

 water or wind ; 2, infiltration of water, carrying and depositing the finer particles in an oblique 



Geol. 3d DisT. 10 



