Handbook of Paleontology 187 



State Survey are known as formation maps. A key 

 to the color scheme accompanies a geological map. 

 This is known as the legend and consists of small rec- 

 tangles colored to correspond to the colors on the map 

 and usually arranged in an ascending series from the 

 oldest to the youngest rocks. Often some pattern is 

 used with the color and perhaps in addition some form 

 of notation as the numbers used to denote each sys- 

 tem on the geological map of North America and the 

 letters used to denote formations, as Do for the Onon- 

 daga formation of the Devonian, and Sm for Silurian 

 Manlius etc. In figure 20 is seen a geological map of 

 New York State showing the surface expression of 

 the various systems of rocks, and accompanying cross- 

 sections are shown in figures 21, 30, 44. Geological sec- 

 tions accompanying geological maps show the true rela- 

 tionships of the various systems or formations. They 

 may be natural cross-sections, columnar sections or re- 

 stored sections. The cross-section shows the profile 

 of the country and the position and structure of the 

 rocks beneath as they are at the present time. They 

 may be drawn with the same vertical and horizontal 

 scale or the vertical scale may be exaggerated, some- 

 times five and ten times as much as the horizontal 

 scale, where the section made is of great horizontal 

 extent. A columnar section shows the vertical suc- 

 cession of rocks. If one imagines a shaft sunk through 

 a series of horizontal strata the sides of the shaft would 

 constitute a columnar section of the rocks cut through. 

 These sections when drawn to scale are important 

 records. Such sections from different regions show 

 variation in the character and thickness of the rock 



