GEOLOGICAL MAP OF NEW-YORK, 
The accompanying Geological Map of the State is intended to present a clear idea of the general 
geological divisions which have been enumerated in the reports. In a few cases it has been found im¬ 
practicable, from the small scale of the map, to indicate all the subdivisions. Thus the lower limestones 
(Birdseye and Trenton) are blended in one color. The same course has been adopted in relation to the 
Helderberg division, where the small extent of surface occupied by each member would preclude the 
indication by separate colors. There is no difference in color to indicate the line of demarkation between 
the Portage and Chemung groups, and in truth there is no distinct line of separation in lithological cha¬ 
racters between the two. All cases of decided change in lithological character are indicated by color. 
That part of the map appertaining to the Fourth district presents a series of almost parallel lines of 
color, showing the limits and the undisturbed range of each formation, rising one above the other on 
the south in a series of steps or terraces. 
The tabular arrangement of colors in the margin, will indicate the formation marked by any par¬ 
ticular color upon the map. The transverse sections at the bottom of the map, colored in the same 
manner, illustrate very satisfactorily the order in which the strata naturally overlie each other. From 
these alone, the map will be understood without consulting any other explanations, except in cases where 
there is disturbance or derangement of the strata. 
The Carboniferous strata within the State are only in isolated patches, consisting of the conglo¬ 
merate and associated sandstone. In some of the maps, a portion of the State of Pennsylvania has been 
colored under the direction of Prof. H. D. Rogers, and this illustrates more clearly the connexion 
between the rocks of New-York and the coal-bearing strata of Pennsylvania. 
The coloring is continued beyond the Niagara river, showing the undisturbed continuation of the 
rocks of the Fourth district into Canada. 
