38 ' ButLETiN 4 152 



' Additional Remarks and Deductions. 

 Nonconformability. 



The marked paleontological break between the Cretaceous and 

 basal Eocene as represented in the Mississippi basin, has, we 

 believe, strongly impressed itself upon all our Neozoic paleontol- 

 ogists. That this break should be so complete while no authen- 

 tical accounts of stratigraphic nonconformity were recorded, 

 seemed indeed anomalous. This deficient record is doubtless 

 chiefly due to three causes: ist, lack of paleontological knowledge 

 on the part of field geologists, causing them to be unable to locate 

 within a fair approximation of accuracy the dividing line between 

 different formations of similar lithological characters; 2d, paucity 

 of contact exposures; 3d, limited extent of such exposures. 



Concerning the particular contact line in question only a few 

 notes will be given, all taken from the writer's personal obser- 

 vation. 



Texas. -^On the Brazos river there is a bed (see p. 14) one foot 

 thick of doubtful age that divides the Midway from the Creta- 

 ceous. The exposure is too limited to determine definitely 

 whether there is discordance or not in the stratification of the 

 respective formations. 



Arkansas. — A few years ago the writer* called attention to the 

 fact that in this State the Cretaceous system is overlayed by 

 Midway Eocene deposits to the northeast of Rockport while to 

 the southwest the Cretaceous comes to the surface in a large 

 > -shaped expanse. This shows, however construed or explained, 

 that the two systems are nonconformable to each other. 



Tennessee. — Unfortunately we did not find any actual Creta- 

 ceous-Eocene contacts in this State, but so far as can be judged 

 from Dr. Safford's specimens and notes the stratigraphy along 

 this line is precisely the same as in Mississippi. 



Mississippi. — At Chalybeate the spring below the Academy 

 issues from beneath an Eocene limestone layer resting directly 

 upon typical upper Cretaceous marl (see p. 22). Here the foliage 

 is so dense that it was not possible to say whether there was 

 stratigraphic nonconformity or not though the break lithologically 

 and paleontologically was complete. 



In a ravine on Mr. Bobo's land, ij^ miles N. N. E. of the 

 spring, the basal bed of Eocene limestone was cemented to an 

 underlying limestone of the same physical aspect bearing Exo- 

 gyrcz and Baculites. The contact line was marked by a row of 

 large quartz pebbles. 



* Ann'l Rep't Geol. Surv. Ark., 1892, vol. ii; publ. 1894, p. 185. 



