An isolith is a line denoting the aggregate thickness of beds of only one 

 lithology in a stratigraphic succession composed of one or more lithologies. 

 Where only one lithology is present, an isolith and an isopach of the same 

 stratigraphic interval are identical. Thus, a sandstone isolith in a series of 

 sandstones, shales, and limestones is a line of equal thickness (isopach) of only 

 the sandstone portion of the section. 



By this definition, an isolith map is a contour map depicting the thicknesses 

 of an exclusive lithology over the map area. Basically, it is an isopach map 

 of one lithology. In a section composed of sandstones and shales, two isolith 

 maps are required to show the total thickness distribution, whereas only one 



*zzzSSS 



V^:/rt^-;m 



JWi 1t. 



Arkcse, Sittstone,,Ss. 



Lime., Qyp., Silt. 



I/irne., Dola, Silt. 



Ark., Gyp., Silt. Lime., Silt. Ltme., J>olo. 



Figure 24-28. Combination isopach and lithofacies map, 



486 



