ORIGIN OF GLAUCONITE. 97 



greenish sand and clay with shells and trilobites," but no particular notice is 

 made of the occurrence. 



Professor Hall* found in the Potsdam of Wisconsin, especially near 

 the base of the formation, "extensive beds of a bright green-colored sand," 

 and observes "that the most strongly colored portions contain few or no 

 fossil remains." Professor Hall also recognized similar green material in 

 collections from Texas. 



In Canada the rocks of the Quebec group (Lower Silurian) are in 

 some localities characterized by grains of a soft green mineral which 

 closely resembles the more recent glauconites, and analyses and descriptions 

 of glauconite from more recent formations in America are given at length 

 by Dr. Hunt in the Report of the Canadian Geological Survey.f 



In the lower magnesian limestone (Canadian) of Minnesota, Dr. OwenJ 

 describes layers of a green mineral called by him a silicate of iron, an 

 analysis of which shows its resemblance to recent greensand. 



The material is so abundant in many of the geological formations that 

 it is a matter of surprise that its source was for a long time unknown, 

 and its mode of formation is still in doubt. To the great microscopist, 

 Ehrenberg, belongs the credit of discovering that the grains of greensand 

 are the casts of foraminifera. This he announced from an examination 

 of the greensand matrix adhering to a bone of Zeuglodon from Alabama, 

 and (in the Monatsbericht, Berlin, February, 1855) he states that "green- 

 sand, in all the numerous relations in which I have as yet examined it, has 

 been recognized as due to the filling up of organic cells." These observa- 

 tions were repeated by Professor Bailey, who examined also Cretaceous 

 greensand from different parts of the United States, and he arrived at the 

 same conclusions as Ehrenberg. Bailey also, in studying specimens of 

 deep-sea soundings from the Atlantic coast in which "black sand, probably 

 greensand," was found with globigerina ooze, states :§ 



That not only is greensand present at the above locality, but at many others, both 

 in the Gulf Stream and Gulf of Mexico, and that this greensand is often in the form 



* Geological Survey of Wisconsin. James Hall. Vol. l,p. 16. 

 + Geology of Canada, 1863. p. 48S. 



X Geological Survey of Wisconsin, Iowa, and Minnesota. D. D. Owen. p. 60. 

 § On the origin of greensand and its formation in the oceans of the present epoch. T. W. Bailey. 

 American Journal of Science. 2, xxii, p. 280. 



7B H 



