176 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



the earth in recognizable form, being entirely consumed, while of 

 those that do survive but a comparatively small number are ever 

 found. Ward, in his summary of 1904, gave the number of distinct 

 falls and finds recorded, and of which specimens have actually been 

 held in human hands, as 815. The total weight of meteoric matter 

 annually added to our earth, a considerable part of it probably as 

 mere meteoric dust, has been estimated at 100.000 tons. 



Meteorites, as they come to us, are unquestionably fragments. In 

 many instances, perhaps in most instances, their final breaking up 

 took place after entering our atmosphere, and to this is due the 

 explosion which is an almost invariable accompaniment of a meteoric 

 fall. The smallest recorded meteorite constituting an entire fall is 

 that of Miihlau in Austria, which weighed 5 grams; the largest is 

 the monster iron brought by Commander Peary from Cape York, 

 Greenland, in 1897 and which weighed some 37£ tons. Second only 

 to this is the so-called Bacubirito iron, a large, scalelike mass lying in 

 Sinaloa, western Mexico, which may perhaps weigh 15 to 20 tons. 

 Both of these, it will be noted, are irons. The largest known indi- 

 vidual meteoric stone is that of Knyahinya. Hungary, which weighed 

 293.5 kilos or 645 pounds. 



All meteorites thus far found are unquestionably of igneous origin. 

 It is customary to divide them upon lithological grounds into three 

 classes which merge into one another, however, by all gradations. 

 These are: (1) Those of an almost purely metallic nature, composed 

 mainly of nickel-iron with nickel and iron phosphides and sulphides 

 which are known as siderites. The Casas Grandes iron, weighing 

 some 3,407 pounds (pi. 2) is a good example of this type. (2) Those 

 consisting of a spongy mass of iron inclosing silicate minerals and 

 known as stony irons, siderolites, or pallasites, like that of Mount 

 Vernon, Kentucky (pi. 3). (3) Those which are essentially stony 

 throughout and known as meteoric stones or aerolites of which that 

 of Modoc, Kansas (fig. 1, pi. 4), is a good illustration. These classes 

 I will consider in the order given, but will first refer briefly to the 

 kinds of elementary matter the meteorites contain and their form 

 of chemical combination. 



Out of the more than 40 elements that have been reported as found 

 in meteorites, the presence of the following, named in alphabetical 

 order, may be considered as fairly well established: Aluminum, 

 argon, calcium, carbon, chlorine, chromium, cobalt, copper, helium, 

 hydrogen, iridium, iron, magnesium, manganese, nickel, nitrogen, 

 oxygen, palladium, phosphorus, platinum, potassium, radium, ruth- 

 enium, silicon, sodium, sulphur, titanium, and vanadium. These 

 are all constitutents of our own sphere also, though their mode 

 of combination is in some cases radically different. In the list given 

 below, the minerals of meteorites are divided into essential and acces- 



