490 April 21.. 
Lesley.] 
blue, representing the Uimestone valley formations, Lower Silurian, Nos. 
ILand IIT of the Pennsylvania nomenclature. 
The Oneida Conglomerate, Shawngunk Grit, and Medina Sandstone, 
Middle Silurian, No. IV, are left uncolored, to make their mountain 
character more conspicuous. The Upper Silurian, Clinton, No. V, carry- 
ing the Dyestone, Fossil Iron Ore, is colored red, to catch the eye, because 
of its practical importance for railway purposes, and because it is the red. 
formation of the North, par excellence, although it is not so marked in 
nature along its southern outcrops. If the native coloring of the soil 
were to govern the tinting of the map the Hudson River slates (No. I{1) 
would require this pigment. 
The Devonians are represented by a Vandyke brown wash (Nos. VITT.. 
IX, X), and the Coal Measures by a wash of Payne’s gray. No color is 
allowed for No. XI., which shows so prominently on the geological map: 
of Pennsylvania in red, because its outcrop is feeble here and not espe— 
cially ved. 
The main features of the topography are quite correct (except near its 
sastern end, of which I can say nothing); and it distinctly shows how 
the mountains are made, by the downthrows, to run in pairs, with a ‘poor 
valley’? between each pair, consisting of Devonian Sandstones and Upper 
Silurian shales containing the Clinton, Dyestone, oi Fossil Iron Ore ; and. 
how the pairs are separated by wider Lower Silurian limestone or ‘rich’ 
valleys, contéining the villages and farms of blue grass and scattered: 
and probably extensive deposits of Brown Hematite [ron Ore, which I 
have not colored. 
The black lines 1, 2, 3, 4, &c., show where the vertical geological sec- 
tions in this report are to be looked for on the map. 
There is no map of this country worthy of the name. [ have copied 
the State map and then changed its details according to my observations. 
The geology is perfectly simple, when one has the key to it. The key to, 
it is given by the pairing off of the mountains along the Downthrows. 
[ begin then with this curious and all important phenomenon. Fig. 1, 
shows it in a purely ideal way ; but reference must be made to Sections 
1, 2, 3, 4, &c., for its actual representation in different places. 
Fie 1. 
IDEAL CROSS SECTION, SHOWING THE CRACKS OR DOWNTHAOWS 
What the power was, which cracked the anticlinal and synclinal curves, 
