BARKIS — OUR LOCAL GEOLOGY. 23 



Prof. Hall* recognized the shales and shaly limestone underlying the 

 encrinal limestone, giving a section of fifty or sixty feet as follows: 



Encrinal limestone, lo — 15 feet. 



Shales and shaly limestone, 50 feet. 



Since his visit, resting on the encrinal limestone, a ijiiarry has been 

 opened in the upper limestones and shales showing a further height of 

 ten feet. Another addition is effected through the change wrought in 

 the encrinal limestone. As it Jiere appears it is a single huge, solid 

 block thirty feet in length and ten to twelve in height, apparently 

 capable of resisting all ordinary elements of change or decay. Yet as 

 we ascend the ravine we find that for nearly a mile the beds and banks 

 of the little stream are strewn with thin layers of the limestone from 

 an inch to two inches in thickness, their surfaces covered with cri- 

 noidal columns and occasional well-preserved smaller corals and bry- 

 ozoa. The fall in the stream for a mile should be taken into account, 

 as it adds further to the height of the rock. The exposure suggests 

 the changing horizons of the three ravines so far noticed. The First 

 cuts into the extreme upper part of the upper limestones and shales. 

 The Second ploughs still deeper into the central portions. The Third 

 finds its way into and through the encrinal limestone, 'i'wo peculiar 

 exposures of the upper limestones should not be overlooked. They 

 occur a quarter of a mile west, just above where the little stream run- 

 ning through the Spirifer Parryanus bed crosses the bluff. In its bed, 

 and covering the entire width of the stream for a short distance, is a 

 rock roughened with the remains of large Orthocera and (lOmphocera. 

 One of the latter was found in excellent condition. This rock may 

 be the extension of the coral reef referred to before, and best exhibited 

 in the Fourth and Sixth Ravines. One thing is certain : a Gompho- 

 ceras of similar size, and in the same relative position, is found in both 

 ravines. A short distance above this rock is found a mass of soft clay 

 abounding in perfect forms of a large ( )rthis, large and small Sfrophe- 

 odonta demissa, and, in a higher portion, abundance of Blothrophyllum. 

 It is most probably the only exposure above the encrinal limestone 

 where large brachiopods have been found. 



The Fourth Ravine is about one mile east of Buffalo. Prof. Hall 

 found there the same series of beds described in the Third Ravine, 

 with the encrinal limestone at the upper part, having a thickness of 

 fifteen or twenty feet. The knowledge since obtained, and the appar- 



* Geology of Iowa, Vol. L, page 86. 



