20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



H. Wanke commented as follows about the Keen Mountain iron 

 in private communications: "The terrestrial age of this meteorite 

 according to argon-39 and chlorine-36 measurements is 1100 ±200 

 years. I had a little problem with my standards, but this definitely 

 would not change the value of the terrestrial age more than 200 

 years. The argon-39 content of this meteorite is so low that it 

 must have been 3 half-lives of argon (T^ = 325 years) on the ground." 

 A statement based on a measurement should be superior to an opinion 

 about the time needed to alter a fresh flight crust from black to brown. 

 However, 900 years seems a long time for fresh flight crust to survive 

 in a climate as damp as that of Virginia. This iron may be an example 

 of a hexahedrite falling into a cluster of an old hexahedrite fall. 



The Walker County, Ala., iron was found in 1832, which makes 

 it the first of this group to be discovered. The data on it came from 

 Farrington's (1915) translation of Cohen's discussion in Meteoriten- 

 kunde (1903) : "an iron mass of 75 kg. weight was found in 1832 in 

 the northeast corner of Walker County, by a hunter living in Morgan 

 County who preserved it in his house until 1843, ... It was of 

 an irregular oval form, with a smooth exterior covered with a thick 

 coating of rust. . , ." 



The alteration (rust) on the Walker County iron might mean a 

 long terrestrial exposure. However, rust could have formed during 

 the 10 years the specimen was stored in the cabin. Some irons 

 exposed to high humidities corrode faster than ones remaining out- 

 doors where the rain washes off the iron chlorides. Hence, the rust 

 in this instance could represent corrosion products formed within a 

 few years. 



The New Baltimore and the Pittsburgh irons should be mentioned 

 here even though they are not listed in table 6. These meteorites and 

 the Mt. Joy iron were found in a straight line across Pennsylvania, 

 and suggested to R, W. Stone (1932) that they were related. A sub- 

 sequent investigation by Henderson and Perry (1958) indicates that 

 these are unrelated meteorites. 



The unique feature of the New Baltimore iron is the large inclusion, 

 about 5x6 cm., with an octahedral pattern enclosed by large kamacite 

 grains. The kamacite grains display well-developed, undisturbed 

 Neumann lines, indicating that this kamacite was neither heated nor 

 deformed since these lines formed. 



It is difficult to explain the mechanism that produces a meteorite 

 with two different types of Ni-Fe alloys in contact with each other. 

 The possibility of the octahedrite colliding with and penetrating a 



