92 Agricultural Geology. 
When freshly excavated, the mass is tough, and breaks irregu- 
larly, some portions only exhibiting a slight tendency to slaty 
structure. After weathering for a short time, it cracks in all di- 
rections, and soon falls into innumerable angular fragments, when 
the disintegration goes on till it forms the soft clay. This change 
seems due to the intimate mixture and decomposition of iron pyr- 
ites in the rock; and its presence is also indicated by the production 
of sulphate of alumina, on decomposition in favorable situations, 
and upon calcination. In tolor, aspect, manner of weathering, 
and other properties, it closely resembles the shale of the upper 
part of the Hamilton group in the Fourth District. Neither are 
micaceous, and both are slightly calcareous, probably from the 
great amount of organic matter. The Niagara shale, however, 
is destitute of those spheroidical concretions, which in the Hamil- 
ton group are more or less common, and in many places abundant. 
The only approach to a concretionary form seen in this shale, is 
in the increased thickness of some layers of impure limestone; and 
this appears rather due to a greater development of corals or oth- 
er fossils, around which the mud accumulated more fieely than 
elsewhere. A few such examples may be seen in the banks of 
the Genessee at Rochester. 
The lower part of this shale is mostly free from calcareous 
bands; while towards the middle and in the upper part, we find 
numerous thin, wedge-form or continuous layers of impure lime- 
stone, mostly composed of corals and other fossils, and their sur- 
faces covered with the same, forming beautiful and interesting 
specimens for the cabinet. The perfect similarity of these with 
specimens from Dudley in England together with the identity of 
many of the organic forms, renders the conclusion unavoidable that 
the two are formations of the same age. These layers are from half 
an inch to two inches thick; and from the decomposition and sinking 
down of the shale, they are usually found broken into fragments. 
One of the most striking features of this rock, is the abundance 
of its fossils. Scarcely a locality can be examined where ihey 
do not occur in great perfection. 
The higher beds are well developed in the falls at Wolcott Vil- 
lage, and the lower part of the formation can be examined by fol- 
lowing down the ravine for a mile. This is the most eastern lo- 
cality in the district where we find the rock exposed. West of 
this point, throughout the county, it is seen in all the small 
streams which flows into the lake. 
