Geological Papers, 89 



deposited that it was near a coast line, and the different layers of 

 shells, followed by shales, would clearly show that the animals had 

 been killed by the overflows of mud. Then the water becoming 

 normal again and teeming with life, again overflowed. Finally the 

 sea became deeper and the Florena shale was deposited; then the 

 shelly layers of impure limestone, and flnally the deeper waters for 

 the formation of the heavy limestone at the top of the Florena 

 shales. The Cottonwood limestone makes no outcrop for several 

 miles to the north; the limestone at the top of the Florena shales 

 making an outcrop which is fairly easily followed, and its nearness 

 to the Cottonwood limestone, makes the mapping of the one prac- 

 tically the mapping of the other. On the west side of the creek 

 above described, in many deep ravines coming into the creek for a 

 mile or so, frequently the same formation as described above is 

 found. 



CONCLUSIONS. 



It would appear from the facts observed in the changes in the 

 lithographical structure of the Cottonwood limestone that the out- 

 crop of this formation was near the margin of the sea at the time 

 the material was laid down. The first change noted being in the 

 top part of the layer, and it gradually becoming more and more 

 shaly, would indicate that the land was rising here to the east of 

 the most eastern outcrop near the head of Jacobs creek, and that be- 

 fore the stratum was completed the water was filled with mud, thus 

 in this way producing the shaly limestone at the top. It was gen- 

 erally observed that where the creeks cut far back to the west the 

 limestone was more normal in its characteristics. The chert in the 

 limestone would indicate that it was formed near the margin of the 

 sea. From the manner in which the chert is found in the forma- 

 tion it is evident that it was deposited in the layer while it was in 

 the process of being formed. The highly fossiliferous shale im- 

 mediately above the Cottonwood limestone certainly shows the land 

 to have been rising and to have come above the depth for the 

 formation of the limestone, and the life to have been exterminated 

 by the muddy deposit now forming the Florena shales. The litho- 

 logical characteristics of the layer after passing into the Verdigris 

 and farther south, where the molluscan part of the layer disappears, 

 strongly reminds one of coquina as formed on the Florida coast 

 to-day. It is this molluscan layer that changes into, the layer con- 

 taining much iron and made up of materials which in some places 

 are very hard and in others very soft, and when exposed by erosion 

 causes the stones on the outcrop to appear very rugged and rough,. 



