186 New York State Museum 



ing a series of formations in a number of different 

 localities and by piecing these sections together, a 

 complete record of this portion of geological time may- 

 be obtained as the sections studied are likely to sup- 

 plement one another. 



Geological formations are recorded on a geological 

 map, which has a topographic map as a base. The 

 more common type of geological map is the one in 

 which the formations are drawn continuously even 

 over regions where there are no outcrops. Contacts 

 not seen may be indicated by a dotted line. Struc- 

 tures such as faults etc. are shown, and fossil localities 

 may also be indicated. The other type of geological 

 map shows only the outcrops with dips and strikes 

 indicated and also other structures as faults etc. A 

 geological map may show only the rock structures, or 

 account may be taken of the surface conditions. The 

 former is the more easily read map, but is to a certain 

 degree misleading to a field explorer, since actual out- 

 crops are not shown ; in the latter, an overprint or 

 over-coloring indicates the surface material and leaves 

 the actual outcrop areas untouched. In the former 

 type of map actual outcrop areas may be indicated by 

 deeper coloring. Whichever the type of map used it 

 embodies the geology of the area as interpreted by the 

 geologist from the outcrop map made in the field. 

 Geological maps showing only outcrops of the several 

 geological systems (Cambrian, Ozarkian, Canadian, 

 Ordovician, Silurian etc.) are known as system maps; 

 those showing the formations, such as the folio maps 

 published by the United States Geological Survey and 

 the large scale map sheets published by the New York 



