3^ UNIVERSITY OF MISSOURI STUDIES 



A little shale was noted near the base of the Gasconade. It 

 was dark gray in color on a weathered outcrop, and was very 

 thin-bedded. Only one exposure was found. 



The dolomite and sandstone show several important struct- 

 ural features, such as ripple-marks, cross-bedding, mud-cracks, 

 oolites, and stylolites. Mud-cracks, oolites, and stylolites were 

 found in the dolomite, and the other features in the sandstone. 

 Ripple-marks, seven inches from crest to crest and one inch in 

 amplitude, were seen. Cross-bedding is common, especially in 

 the upper part of the formation. Some of the mud-cracks were 

 at intervals of from four to six inches. Some were from one- 

 half to one inch wide, while others were only one-eighth of an 

 inch wide. The stylolites were rarely over one inch long. 



The chert is found ( 1 ) in layers interbedded with the other 

 members of the formation, especially dolomite; (2) in nodules 

 of large size along the bedding planes; and (3) as small irregu- 

 lar masses and nodules in the dolomite. Most of it is white or 

 light gray, but dark grays and blacks are seen, and the weathered 

 product is usually stained some shade of yellow or red by the 

 iron oxides. The chert is always dense and tough, breaking with 

 a straight to subconchoidal fracture, rarely with a perfect con- 

 choidal fracture. Much of the chert is banded, the bands being 

 concentric in some instances, in others rudely parallel to the bed- 

 ding planes or lamellae. Rarely the chert is in rounded elliptical 

 forms, 8 to 15 inches in diameter. These forms show splendid 

 bands which are accentuated by differential weathering. They 

 are well exposed in the beds of some of the streams flowing on 

 the Gasconade formation. Not infrequently there are narrow 

 elongated cavities lined with drusy quartz in the bands of the 

 chert. These shapes are strongly suggestive of lithophysae, but 

 are not so continuous as the concentric shells of the latter. 



Oolitic chert is a common constituent of the Gasconade 

 formation. This fact is a great help at times in locating the 

 lower limit of the formation. The oolites are silicious, and the 

 microscope shows that most of them are perfectly rounded, but 

 some are elliptical, and all are more or less embedded in chalce- 

 dony and quartz. They average from .4 to .5 mm. in diameter. 

 In places they are cemented with limonite and hematite. The 



