[Assembly 
The design in the execution of this map has been to give a condensed 
view of the principal rock strata exposed along the Genesee river, and 
the streams flowing into it between Portage and its mouth. On a map 
so narrow, it was found impossible to observe that relative distance be- 
tween points which on a topographical map would be required. Seve- 
ral views on the smaller streams, whose distance from the river is so 
great as to exclude them from a representation upon the map, have been 
brought in, as at West Mendon and the falls near Le Roy. And again, 
at York, Avon, Geneseo, and Mount Morris, the relative distances re- 
spectively have been greatly increased. But little regard has been given 
to any thing else than the exact order of succession in the rocks, as they 
are exposed in the views here given. This species of projection requires 
that the map be so viewed that the names of the rocks along the river 
will be read in their proper position. 
The detailed examinations in the fourth district this season have been 
confined chiefly to the four counties bordering on Lake Ontario. 
The rocks in these counties occur in the order in which they are de- 
scribed; the upper or gypseous rocks forming the southern boundary of 
each of the four counties. The description of each rock is distinct 
from the local and economical geology of the same, for the convenience 
of reference. Under the latter head will be discussed the economical 
value and utility of each rock and its contents. 
SECTION I. 
Red Marl and Sandstone.* 
This formation extends from the eastern boundary of Wayne county 
to the Niagara river, the limit of our district. Commencing at the Ni- 
agara river, where it is eight miles wide, it becomes gradually narrower, 
and towards the eastern part of Wayne county disappears beneath the 
lake; while at the eastern limit of this county it has again emerged, to 
the height of thirty or forty feet above the lake. 
This rock in some places is extremely coarse grained and siliceous, 
and in others, for a limited extent, approaches a conglommerate. The 
siliceous portions are generally confined to a few of the upper strata, 
which alternate with seams of shale. The upper stratum of this rock 
* The term " variegated sandstone" being already appropriated, as designating a member of 
the new red sandstone series, it becomes inapplicable to this rock, which is afraember of a 
much older formation. Besides this, there are only a few of the uppar strata which are varie- 
gated% 
