14:8 ANNALS NEW YORK ACADEMY OF SCIENCES 



two sliowed ore seams with sliale or clay partings or strata ranging from 

 a fraction of an incli to several hundred feet in thickness above and 

 below. 



Taking u|) tlio artesian conditions found in the Clinton iron ore de- 

 posits more in detail, we find governing factors. 



POROUS LAYKUS 



^J'he first arc the porous strata, or better those which were without 

 doubt originally porous, and which consist of fragmentary rocks such as 

 sandstones now in many cases altered to the oolitic hematite beds. Seams 

 of til is class were personally examined at Clinton, New York, and Big 

 Stone Gap, Virginia. Specimens of oolitic ore with quartz grains as 

 nuclei were also examined from Kentucky and from AVisconsin. Records 

 of similar strata have been found in Ohio and West Virginia. 



Rock slides made from this class of ore show conclusively that the 

 original sediments must have been ordinary shore or near-shore deposits 

 of sand, similar in every way to ordinary marine sand such as we find on 

 our beaches to-day. Sand, loose or consolidated by cementation into 

 common sandstone, forms as perfect a porous medium as could be de- 

 sired for artesian purposes. Some sandstones show as high as 30 per cent 

 pore space. The other principal type of Clinton ore, the fossil ore, con- 

 sists of beds of fossil fragments such as pieces of crinoid stems, corals, 

 bryozoans, brachiopods, and many other varieties of Clinton fossils, 

 deposited by the ordinary processes of sedimentation and later consoli- 

 dated into the usual types of fossiliferous limestones. These furnish, 

 in the earlier stages at least, ideal porous conditions and are quoted by 

 practically all writers on. artesian flows as favorable for water penetra- 

 tion. 



After a close examination of slides of these fossil beds (Plates IX, 

 XVI), it cannot be doubted that for a time at least these layers must 

 have been extremely free runways for penetrating surface waters. Arte- 

 sian reservoirs exist in rocks like the coarsely crystalline limestones, far 

 less favorable than either sandstone or fossiliferous limestone, and there- 

 fore it would appear to the writer that the complete porosity of these 

 layers can hardly be disputefl. 



IMPERVIOUS LAYERS 



Impervious contacts were found, separating two strata of different 

 textures and degrees of porosity. 



As has already been pointed out (page 138), where two porous layers 



