AN AMERICAN GEOLOGICAL RAILWAY GUIDE. 49 



ARRANGEMENT OF THE GEOLOGICAL RAILWAY GUIDE 



AND DIRECTIONS FOR USING IT. 



1. The railroads are arranged by states, and the states and territories are 

 arranged in geographical order, with reference to the great lines of travel. But 

 to find a railroad, the reader must depend on the index. Branches are placed after 

 the main line, which is generally first given throughout without interruption. 



2. When stations are omitted for the sake of brevity, which is seldom the 

 case, the lists being uncommonly full, their geology will be understood to be the 

 same as that given at the stations between which they occur. If the geology of 

 two adjacent stations is different, it is evident enough that there is a transition 

 from one to the other formation, between the stations, but the change is often so 

 gradual that the transition point cannot be precisely given. 



3. A few feet of difference in level sometimes carries the railway track 

 to an upper or lower formation. Railroads, too, sometimes run across narrow, 

 projecting tails, and scalloped points of a higher or lower formation, than that 

 given in the Guide, but which it would occupy too much space to specify. Where 

 too, the strata are disturbed and broken-up, all the formations cannot well be 

 specified for want of room. In such cases the Guide serves only to show nearly 

 where you are, the prevalent formation being given. 



4. The hills, bluffs and higher ground in view, are often of a different 

 formation from that given on the railroad, but not always higher in the series. 

 Their elevation is often due to the hardness of the strata, the softer rocks f orming 

 the valleys, in which railways generally run. 



5. Keep in mind the succession of the formations, as shown on the Guide, 

 and whether you are going from older and lower to younger or higher strata, or 

 vice versa. Notice the changes in the scenery with the changes in the formations. 



C. When you come to a new formation, refer to the description of it, in the 

 beginning of the book. But it is difficult to get a clear idea of the formations 

 from even the best description. The reader must see them for himself, and these 

 descriptions are intended to assist him in identifying them, and to impress their 

 character and appearance upon his mind, or to recall them to his recollection after 

 having seen them. 



7. By a little close observation of the formations in traveling, you will find 

 that most of them have peculiarities of their own, by which you can always 

 know them, but which, like the features or appearances of persons, cannot be put 

 into words, so that another who has not seen them could also recognize them. The 

 form of the summits and slopes of the hills, and the general aspect of the country, 

 but especially the rock-cuts on the railways, and other exposures of the forma- 

 tions, in quarries, and in the banks and beds of streams, should be closely 

 observed ; and if these are not visible, notice the stone used in buildings, and for 

 the enclosures of fields, the character of the soil, and the fragments of stone mixed 

 through its mass, which betray the nature of the solid rock formation beneath ; 

 observe also whether the rocks lie horizontally or in an inclined position. 



