No. 200.] 
grounds throughout the whole of this formation, the extent of which 
may be learned by referring to the description. 
In several places east of the Genesee, in Monroe county, this marl 
has been found in small quantities. The gypseous formation on that 
side of the river is mostly covered with diluvial hills. 
Small deposits of tufa and shell marl are found along the country 
north of the mountain ridge, arising from the decomposition of the calca- 
reous shales above the sandstone. Some of these deposits are of suffi- 
cient magnitude to supply one or two farms with this article for ma- 
nure for a great period of time. 
From the texture and composition of these shales and of the gypse- 
ous rocks, they are more readily dissolved than the solid limestone, and 
it thus happens that little tufa or marl is found on the limestone proper. 
Among the gypseous rocks, the process constantly going on to form sul- 
phate of lime, liberates large portions of carbonic acid, and this is doubt- 
less the cause that deposits of marl and tufa are so much more exten- 
sive in this formation. 
The partially decomposed calcareous shale above the sandstone aflfords 
a good manure for sandy lands, but contains too much clay to be advan- 
tageous on lands which already have that substance. This shale in 
many places contains iron pyrites, which, by its decomposition, produ- 
ces gypsum. This is found from experiment to be eminently useful on 
sandy soils. All the shale readily crumbles into fine particles, and in 
this state could be spread on the soil, where its more complete decom- 
position would be effected by the atmospheric agents, and during the 
process, the required stimuli furnished to vegetation. 
This shale has been quarried at Marshall's mills, in Ogden, ground 
and used on the soil, under the impression that it was gypsum. At this 
place the shale contains pyrites disseminated through it, and from its 
decomposition gypsum would be formed. In many places north of the 
mountain ridge, the shale approaches the surfaces, and could be readily 
obtained for manuring lands. 
The decomposing gypseous rocks afford a marl, which is sometimes 
too clayey to be beneficial as a manure, but in other cases it is valuable, 
especially when mixed with shell marl. This marl approaches the sur- 
face in many places in the town of Pittsford, where it is of a character 
well adapted for use on sandy lands. The same marl occurs also east 
of Pittsford, along the line of the canal, and at Fairport. Gypsum in 
