4 GEOLOGICAL REPORT. [T5 



the exception of the territory occupied by the alluvium of the 

 Mississippi Bottom, and by the Bluff formation of the Southern 

 River Counties, the formations laid down on the map do not, as a 

 general thing, occupy the surface to any considerable extent, nor 

 even do they in most cases, immediately underlie the arable stratum 

 of their region of occurrence. The latter, in most of the better 

 class of upland soils, is formed by a yellow or brown loam, of an 

 age more modern than the Bluff formation (which it frequently 

 overlies), and from two to ten feet in thickness. But the forma- 

 tion which gives character to the surface conformation of the 

 State— whose presence is the rule, and whose absence the exception 

 requiring special mention ; which forms the main body of most 

 ridges, and to a very great extent, their surface also — is that 

 which has been very appropriately designated by Prof. Safford. 

 the State Geologist of Tennessee, as the Orange Sand formation, 

 5. It may appear surprising at first sight, in view of these facts 

 that this important formation should not have been laid down, or 

 even mentioned, on the geological map ; but the very universality 

 of its occurrence has made this a matter of necessity, unless the 

 other formations were to be concealed by it on the map, in the 

 same manner in which they are in nature : so much so, that this 

 very formation is among the most serious obstacles in the examination 

 of the more ancient formations of Mississippi, and that a proper 

 understanding of its peculiarities is the first necessity in the study 

 of the geology of the State. And since even a description of the 

 other formations involves, of necessity, a continual reference to 

 these peculiarities, it may be best to give the special description of 

 the Orange Sand formation, out of its proper order in the geologi- 

 cal series, as a key and introduction to the geological structure of 

 Mississippi. 



