102 MINERALS OF MARYLAND. 



from that made with a salt of peroxide of iron, in being readily- 

 soluble in water ; whereas that made with a salt of peroxide 

 of iron is not soluble in water. I always succeeded in dis- 

 solving both ; but it is true that the blue made with a salt of 

 peroxide of iron requires much more washing than that made 

 with a salt of protoxide of iron to become soluble. 



From the foregoing experiments it appears then, as Mr. 

 Robiquet suggested in a memoir, published in the An?i. de 

 Chim. et de Physique^ torn 44, that the difference we observe in 

 Prussian blue may be attributed to the presence of potassium 

 or potassa, for it is evident that the blue made with a salt of 

 peroxide of iron cannot contain any potassium or potassa, and 

 that made with a salt of protoxide of iron does contain some, 

 unless perfectly oxidated by washing for a long time with 

 acidulated water. 



ARTICLK VI. 



A descriptive Catalogue of the piincipal Minerals of the State 

 of Maryland. — By P. T. Tyson. 



[Read before the Academy, March 9, 1637.] 



For greater convenience and to avoid repetition in noticing 

 localities, the State will be divided into six districts. 



The first, embracing more than half of its territory, which 

 lies south-east of a line drawn from Washington through Balti- 

 more, Havre-de Grace, and Elkton, will be called the Hide-water 

 district.'' Its north-western portion, comprising a narrow belt 

 whose edges are not yet defined, is believed to belong to an 

 upper secondary series, and rests upon the primary rocks of 

 the second of our divisions. It is covered on the south-east 

 by the remainder and larger portion of the first district, con- 

 sisting of the great tertiary deposiles of the United States, 

 which constitute nearly one-half of the territory of the State 

 of Maryland. This region abounds with organic fossils, 

 but its mineralogy possesses little interest. It consists of 

 sands, clays, gravel, and loam (in many places abounding 

 with fossils) and in ihe secondary portion some small beds of 



