292 
[Assembly 
tain several species, among which are the Calymene macropthalma or 
bufo, Asaphus, Crypheus, Dipleura. 
There are other fossils which mark the distinction between the rocks, 
but none of them so characteristic as the trilobite. Our limits at th^ 
present time will not allow further discussion respecting the age and 
position of these rocks. 
Above the shales of the mountain limestone we have (see section) a 
series of shales, grits, sandstones and conglomerates, with thin strata of 
limestone. These extend 80 miles, giving a thickness of 4,000 feet 
before we come to a bed of coal. The limestone shale, particularly 
the upper portions, contain nodules of bituminous limestone and septaria. 
The accompanying map is an application of the principles of Isome- 
trical projection to geological drawings. In this species of projection 
the limits of each formation may be defined, the character of the surface 
represented, the dip of the strata given, the natural sections, &c.* 
The plan was conceived and the map constructed by Mr. E. N. Hors 
ford, of the Rensselaer Institute. 
Geology of the Genesee River. 
From the mouth of the river to Carthage, three miles below Roches- 
ter, the red sandstone and indurated marl are the only rocks. The up- 
per stratum of the red sandstone disappears beneath the river at the 
lower falls. Immediately above these rocks are the green shales, alter- 
nating with which are strata of limestone, and a single stratum of iron 
ore. Next in order of superposition, are the calcareous shales, alter- 
nating with thin strata of limestone, extending to the upper falls, and 
underlaying the Geodiferous and bituminous limestone. The lower lay- 
ers of the limestone constitute the bed of the river at the upper falls. 
Near the feeder dam, scattered about upon the surface, are large angular 
fragments of the rocks in the vicinity. 
Succeeding the limestone are the Gypseous slates and marls, extend- 
ing as far south as Wheatland. A single view of a bed of gypsum is 
given in Wheatland on Allen's creek. 
Upon the Gypseous rocks lies the mountain limestone, commencing 
at Caledonia and near West Mendon, and extending as far south as 
Owing to a miitake of the engraver, the map is left without a margin, which essentially 
injures the effect. 
