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DAVEXPORT ACADEMY OF NATURAL SCIENCES. 



the writer lie could at once recognize the presence of this rock by the 

 peculiar ring it gave back to the stroke of the iron bar, even though its 

 surface was covered deep by water. 



This series of beds, then, seems to be well defined in both its upward 

 and downward limits— the Hamilton above, this " Hint rock" below. Its 

 thickness is variable, averaging from twelve to twenty feet, of which at 

 times one quarter is made up of these upper broken uncontinuous layers, 

 only found, so far, on the Iowa side of the river. 



The following table exhibits not only the succession of strata, but the 

 localities in which such succession has been studied : 



No. 5. Uppermost limit ; loose masses of coral scattered over the 

 surface. 



No. 4. Thin strata of shattered broken layers ; crowded with valves 

 of BenssellcBria and remains of Crinoidea ; thickness three to four feet. 



Xo. 3. Bed of compact mass of casts of Renssellceria ; thickness one 

 and one-half to two feet. 



No. 2. Dove colored compact limestone ; ten to twelve feet. 



No. 1. Concretionary; thickness unknown. 



Presence in quarry denoted by a *. 



(1) In thin layers. (2) Scattered on surface. (3) Consolidated into reef. 



One of the most marked characteristics of these beds is the frequent 

 recurrence of large cavernous openings of greater or less extent and 

 irregularity. They have the appearance of having been worn out by the 

 action of running water. They are filled with foreign material, derived, 

 no doubt, from higher rocks in the series. Prof. Hall, in his Geology of 

 the vState of Iowa, Vol. I, pp. 84 and 130, has called attention to and de- 

 scribed several such instances occurring in the Helderberg. In the 

 quarries we are examining, these reservoirs of foreign material may be 

 resolved into three classes, referable to the material with which the cav- 

 ity is filled. 



First are those filled with sand and sandstone. This sand exists in 

 very fine grains, of a white or greyish white color, occasionally stained 

 with iron. In some portions it is no unusual circumstance to find peb- 

 bles and rolled stones. So far no fossils have been discovered in it 

 belonging to the mass. It is most probable this sand has filtered through 



