THE TOMAH AND SPARTA QUADRANGLES 629 



Relations to the St. Lawrence formation. — In many places it is 

 extremely difficult to locate the surface of division between the 

 St. Lawrence and Jordan formations. Locally the strata assigned 

 to the Jordan begin with a long, fore-set, cross-laminated stratum 

 which in comparison with the more horizontally laminated St. Law- 

 rence makes the contact quite conspicuous. In some exposures a 

 thin layer of conglomerate marks the contact. In their larger 

 relations the two groups of rocks are quite different, the bedding of 

 the Jordan being much more irregular '*knd the sands more coarse 

 than obtain in the St. Lawrence. The writers have observed no 

 decisive evidence in this area that the St. Lawrence strata were 

 eroded before the deposition of the Jordan. 



Characteristics. — The Jordan formation in these two quad- 

 rangles consists wholly of sandstone. The textures vary from 

 coarse to fine and the colors from gray to light brown. The 

 sorting is generally not good. Some beds contain an abundance of 

 fine-grained sandstone pebbles. A characteristic feature is the 

 presence of calcareous concretions with diameters varying from a 

 fraction of an inch to about 2 inches. The bedding is massive and 

 extremely irregular. Cross-lamination and cross-bedding are 

 present throughout, some of the fore-sets being up to 50 feet in 

 length and having angles of inclination for such lengths up to 25°. 

 Directions vary, but the writers' observations indicate a dominance 

 of inclination in a southerly direction. No fossils have been ob- 

 served in this formation in either of the two quadrangles. The 

 thickness varies from about 20 to about 40 feet. 



Conditions of origin. — ^There is no known evidence in either of 

 the two quadrangles to indicate that the Jordan sandstone is of 

 marine origin. Parts of it appear to have been deposited by the 

 wind. To the writers it appears probable that the formation 

 represents the emergent deposits consequent upon the complete 

 withdrawal of the waters from the sand flats postulated for the 

 times of the preceding formations. 



THE MADISON (?) FORMATION 



Overlying the sandstones which have been identified as belong- 

 ing to the Jordan are other sandstones which in some respects 

 resemble those of the Madison formation. These sandstones are 



