FRESH WATEE FAUNA. 167 



rocks. Their mode of occurrence everywhere shows evidence of shallow 

 water, but they rapidly pass into beds indicating much deeper water. 

 Associated with these fresh-water shells are numerous fragments of plant 

 remains, proving, without doubt, the existence at no great distance of a 

 land surface. The specific characters of these shells will be found described 

 elsewhere by Mr. Walcott. 1 



Limestone of Richmond Mountain. Between Eureka Canyon and Richmond 

 Mountain lies a body of limestone uniformly inclined to the east until it 

 passes beneath the andesites of the latter mountain. It rises nearly 700 

 feet above the valley, with a fairly regular slope, except where trenched by 

 short drainage channels which have cut deeply into the rock, giving the 

 ridge a somewhat ribbed appearance. The beds strike N. 16 E. and 

 dip from 40 to 50 under the lavas. The Richmond Smelting Works are 

 situated near the northern end of this limestone body. Just back of the 

 smelters the base of the limestones are well exposed, and near the rail- 

 way cut there may be seen a good exposure of strata. At the base of 

 the cliff occurs a series of dark argillaceous shales of unknown thickness 

 weathering 011 exposure to blue and gray clays. In these clays may be 

 found indications of plant remains associated with the Physa prisca and 

 Ampularia obtained on the opposite side of the ravine in New York Hill, 

 the shells serving to correlate the beds. It is to be regretted that their 

 strike and dip could not be determined with precision, but they give every 

 appearance of passing conformably beneath the overlying strata. 



The following section was made across the strata extending from the 

 top of the series down to the clay beds at the base: 



Feet. 



1. Coarse conglomerate cemented in fine arenaceous grains 50 



2. Compact gray and yellow sandstones carrying a little calcareous material, 



and occasional thin belts of limestone 200 



3. Fine smooth pebbles in a yellow matrix 100 



4. Brownish white sandstone 



5. Fine conglomerate, with an admixture of calcareous material throughout- 100 



6. Gray limestone, passing into a light gray and yellowish sandstone . 75 



7. Cherty limestone, passing into fine siliceous limestone 73 



8. Light colored and banded vitreous quartzite 25 



1 Paleontology of the Kureka District, Mon. vin, U. S. Geolo>tH'l Survey, p. 261. 



