124: 



AQUEOUS EOCKS 



in beds which, when compared with other rocks of the earth's 

 crust, are of comparatively insignificant proportions, but which 

 are nevertheless of considerable geological importance. Though 

 deposits of this material are still forming, and have been formed 

 in times past at various periods of the earth's history, they 

 appear most abundantly associated with the Tertiary formations. 

 The beds are wide-spread, and some of them of economic 

 importance. A deposit in Biln, Bohemia, is some 14 feet in 

 thickness, and is estimated by Bhrenberg to contain 40,000,000 

 shells to every cubic inch. Beds occur in the United States at 

 South Beddington, Maine; Lake Umbagog, New Hampshire; in 



Fig. 10. — Section through lake basin showing the formation of diatomaeeoua 

 earth. «, bed rock; &&, floating peat; cg, decayed peat; d, diatomaceous 

 earth. 



Morris County, New Jersey; near Richmond, Virginia; in Cal- 

 vert and Charles counties, Maryland; in New Mexico; Graham 

 County, Arizona; near Reno, Nevada, and in various parts of 

 California and Oregon. 



Chemically the rock is impure opal, as shown by the following 

 analyses of samples from (I) Lake Umbagog, New Hampshire, 

 (II) Morris County, New Jersey, and (III) Pope's Creek, Mary- 

 land: 



Chemical Composition of Diatomaceous Earth. 



CONSTITTJBNTS 



Silica (Si02) 



Iron oxides (FeaOa and TeO) 



Alumina (AlaOg) 



Lime (CaO) 



Water (H2O) 



Organic matter 



80.53% 



1.03 



6.89 



0.35 

 11.05 



0.98 



99.83% 



II 



80.60% 



3.84 



0.58 



14.00 



99.02 % 



III 



81.53% 

 3.33 

 3.43 

 2.61 

 6.04 



96.94% 



Number III showed also small amounts of potash and soda. 



(2) The Calcareous Group. — These rocks are made np of 

 the more or less fragmental remains of molluscs, corals, and 



