746 NOTES ON NORTH AMERICAN SHELLS STEARNS. 



was that tlicre was a greater density iu that hemisphere and hence a greater attract- 

 ing power for water. This unequal density might bo accounted for hy some unusual 

 accretion there, such as Avould arise from contact with a star. Speculation as to 

 the possibility that the earth's greater hollows originated in this way suggested to 

 him a similar exi)lanati()u for the origin of the Arizona crater, that it was caused 

 by the coliisidu of an iron star several thousand feet in diameter. 



In order to iind out what this theory was worth, Mr. (iilbert, accompanied by Mr. 

 Marcus Baker, visited Coon Mountain and camped near there for some time, carefully 

 studying all the peculiarities of the place, and making a number of observations to 

 discover whether the relation between all this meteoric iron and the crater, was one 

 of cause and effect, or of coincidence merely. Coon Mountain rises some 400 feet 

 above the level of the surrounding plain, and the; bottom of tlie crater is al»out GOO 

 feet below the highest point on the rim. 



The rock strata of the plain are limestone and sandstone and lie nearly flat. In the 

 rim of the crater tliese rocks are bent upward, and ujjon them lie broken fragments 

 of the same materials. The peculiarity of the crater, from the geological point of 

 view, is that it contains no volcanic rocks, and in this respect is unique. The 

 ])hcnomena observable in connection with the crater had given rise to a number of 

 hypotheses, two of which the speaker discussed more freely than the others. The 

 glacial hyi)otliesis and the theory of the limestone sink are both inadequate. The 

 true hyi»othesis of the crater implies the expenditure of a tremendous amount of 

 energy iu a very brief space of time. By the system of elimination all the hypotheses 

 have been abandoned with the exception of the stellar and the explosive. Magnetic 

 and volumetric tests Avere ajjplied, and with the former the needle showed no 

 evidence of the presence of a considerable mass of iron. After experiments with 

 these same needles later it was estimated that if the crater was formed by the pen- 

 etration of such a mass, it must have been buried 50 miles below the surface to have 

 afl'ected the needle so slightly. 



By the volumetric test it was necessary to determine whether tlie d6bris sur- 

 rounding the crater would just till it or exceed the necessary amount by the supposed 

 amount of the embedded star. It was found that it would just fill it, and this would 

 seem to comjtel the aliandoning of tlie stellar tlieory, arid we are forced to believe 

 that the relation of rock and crater is one of coincidence only, though the chances 

 of such a coincidence are not greater than one in five thousand. After comparing 

 the phenomena of Coon Mountain with those of the volcanic eruptions iu Japan in 

 1888, Mr. Gilbert said that iu the future Coon Mountain will probably be looked upon 

 as an examjde of the bursting of the earth's surface by volcanic steam unaccompanied 

 by lava. It is liighly improbable that this catastrophe was witnessed by man. 



From a description of the region and the phenomenal character of 

 the remarkable locality where Mr. Baker collected his examples of 

 strigosa, Ave will retnrn to a fnrther consideration of the shells and the 

 varietal aspect they exhibit. In a recently pnblished portion of his 

 Manual in refering to the .strigosa group of Patula, Mr. Pilsbry says: * 



In the species of this division [Anguispira], the characters of sculpture, form and 

 color and to a less degree of tlu^ soft parts, vary to an extent inconceivable to those 

 who have not actually seen the shells. It may now i)e demonstrated that the forms 

 described as ^. stritjosa, Coojxri, idahoensis, JlemphiUi, Haijdciii, etc., are connected 

 by such a multitude of intermediate forms that it is absolutely impossible by the 

 most acute analysis, to draw lines of demarcation between them. 



It is refreshing in these days of excessive systeniizatiou and species- 

 making to meet with a i)aragraph like the above by an author of Justly 

 recognized ability in a ])ublication of standard character and impor- 

 * Vol. VIII Manual of Conehology jiage 115, Feb. 28, 1893. 



