LITHOLOGK; correlation IX "bend series, TEXAS. 



17 



RELATIVE THICKNESS OF THE SECTION IN THE 

 TWO WELLS. 



The relativo thicknesses of the tiiiits arc pre- 

 sented in the following table: 



The presence of the "Lower Bend" lime- 

 stone in both wells in proportions! tely nearly 

 equal thickness underlying the big unconform- 

 ity that separates it from the Marble Falls 



Relative thiekncs.'ies of units A to L in Rudd and Seaman ireUs. 



There is little to generalize about in this table. 

 The region of the Seaman well, as pointed out 

 on page 6, was nearer than the region of the 

 Rudd well to the old land mass from which the 

 "Bend" sediments were derived: hence the 

 section is much thicker there. In some indi- 

 vidual units, however, this relation is reversed. 

 Tlirough units C, D, and E there is a continu- 

 ous decrease in ratios of thickness with increas- 

 ing deposition of lime, but this relation to lime 

 deposition does not hold throughout the sec- 

 tion. 



It is worth special notice that the dominant 

 thickness ratio applies also to the "Lower 

 Bend" in the two wells, a fact which indicates 

 that appro.ximately the same land supplied 

 sediment to this region during the earlier Mis- 

 sissippian deposition. This fact opposes the 

 assumption, which is also otherwise improba- 

 ble, that unit J derived its sediments from a 

 different source than the overlying members of 

 the Marble Falls. The apparently greater 

 sandiness of parts of unit J in the Kudd weU 

 than in the Seaman well may therefore, for 

 lack of a better explanation, hi^ tentatively 

 attributed to local currents. 



limestone is very surprising. Doubtless the 

 hardness of the "Lower Bend" limestone 

 tentled to preserve it as the siu-face bed, but 

 even so its occurrence in this way, if general, 

 implies a remarkable plana tion before the dep- 

 osition of the Marble Falls. Possibly the posi- 

 tion of both wells near the axis of the ' 'Bend 

 arch" (see fig. 1, p. 6) has something to do 

 with this similarity. It would be interesting 

 to determine whether any relation exists be- 

 tween position on the "Bend arch" and the 

 erosion of the "Lower B(>nd" limestone and 

 shale before the deposition of the lowest 

 Pennsylvanian beds. 



COMPARISON OF THE SYNTHETIC LOG OF THE 

 SEAMAN WELL WITH THE DRILLER'S LOG. 



Mere hasty inspection reveals at once the 

 wide divergences between the synthetic log and 

 the driller's log, the failure of the driller's log to 

 bring out many essential features, and the 

 error in many identifications. In part these 

 errors and inaccuracies are doubtless due to the 

 special dilficulties presented by the section in 

 the Seaman well, particularly to the mixing of 

 ingredients in individual beds and tthe rajiid 

 alternation of beds of different c.om])osition. 



