STRATIGRAPHY. 93 



The Tertiary strata dip southward at an average rate 

 of about 30 feet per mile (an important point to remember 

 when drilling for water or oil), so that the oldest ones 

 crop out farthest inland. A notable exception to the gen- 

 eral southward dip is found in the Hatchetigbee anticline, 

 a gentle fold or uplift in the region of the lime hills, which 

 brings to the surface strata as low down as the Hatchetig- 

 bee, several miles south of their main outcrop, where they 

 would normally be a few hundred feet below the surface. 

 This fold makes an outlying range of small "mountains," 

 with several mineral springs, salt wells, and other curiosi- 

 ties. There are less conspicuous anticlines, accompanied 

 by a little faulting, and causing some irregularities of out- 

 crop, near Lower Peach Tree on the Alabama River and 

 Jackson on the Tombigbee. 



The outcrops of coastal plain strata in Alabama that are 

 recognizable by their fossils or lithological characters are 

 very limited in extent, the greater part of the surface being 

 covered by thoroughly weathered residual material, which 

 looks much the same over many different formations, or by 

 non-fossiliferous beds like the Citronelle, Lafayette and 

 Columbia (the existence of the two last is now questioned 

 by some geologists), and second-bottom deposits, so that the 

 exact boundaries of the different formations between the 

 rivers must always remain more or less hypothetical, and 

 several points are still in dispute. For this reason no at- 

 tempt has been made to provide a geological map for this 

 report; but on comparing the regional map herein with 

 various geological maps hitherto published by this Survey, 

 a pretty close correspondence will be observed, except in a 

 few of the southernmost counties, where rock outcrops are 

 very scarce. 



Economic Geology. 



The Pleistocene and Recent formations contain an 

 abundance of sand and clay suitable for mortar, brick, road 

 material, etc., and in some places pebbles which can be used 

 for concrete or on roads. The ferruginous sandstone ex- 

 tensively used for chimneys and pillars in the rural districts 

 may represent material of almost any age, but it is essen- 

 tially a surface phenomenon, formed in comparatively re- 

 cent (perhaps Pleistocene) time by the action of ground 

 water containing iron compounds which cement the sand 



