METEORITES OF NORTH AMERICA. 29 



WIDMANNSTATTEN FIGURES THE TRIAD. 



The Algoma meteorite is an octahedral siderite rich in kamacite and tenite and relatively poor in pleseite. The 

 kamacite bands are of three types: First, there are the relatively thick hands (0.6 to 1 mm.) which cover the space 

 of the section in a fairly regular network; second, there are parallel series of perfectly contiguous finer bands (0.1 to 

 0.5 mm.) or Kamme, which completely fill the large areas (Cohen's Gescharrter Kamazit), and, lastly, there are the 

 swathing bands about schreibersite (Wickelkamazit), which are usually of exceptional width and generally swollen 

 and irregular as regards outlines. Gradations between these varieties occur, but the firet two types are nevertheless 

 very clearly marked in the general structure. The wickelkamazit frequently, though not always, produces a merely 

 local swelling of the coarser bands. Tsenite in jagged, irregular, and occasionally interrupted lines surrounds the 

 kamacite of all types. The plessite is of the structureless variety (Fleckiger pleseit). 



XEUMAXK LINES. 



The kamacite bands when etched to any considerable depth reveal beautiful Neumann lines (Schraffirter Kamazit). 

 REICHENBACH'S LAXELLS SCHREIBERSITE. 



The schreibersite, which is prominent on etched surfaces by reason of its brilliant luster and it# great suscepti- 

 bility to oxidation, is arranged in rather distinct lines within the kamacite (Reichenbach's lamella). Always envel- 

 oped in kamacite, the largest area within the principal section has a wide aureole of kamacite about it. Being at 

 the front surface of the meteorite, its fusion on one side has produced a noticeable depression on that surface. The 

 hardness of this mineral was at the limit for the band saws used in cutting, even small areas of schreibersite sufficing 

 to break them, and the hardness and brittleneas were, moreover, serious obstacles in the way of securing well-polished 

 surfaces for etching . The analysis shows that schreibersite comprises about 1 per cent of the entire mass of the meteorite. 

 The mineral is developed in relatively thin plates, often of considerable size. The one which figures in all the sections 

 was also encountered in the saw-cut which extends partly through the meteorite at a distance of 2 to 4 cm. from the 

 sawed end, and must, therefore, have been not less than 3.5 or 4 cm. in length. The small branches of this crystal 

 conform to the Reichenbach lines. 



The fractures noticed on the front surface of the meteorite are seen in section on the forward margin of the etched 

 surfaces as local, small dark lines extending into the mass for a depth of 1 or 2 mm. These are evidently filled with 

 an oxidation product (perhaps the "Eisenglas" of some authors). 



Owing to the markedly swollen character of the kamacite bands (Wulstiger Kamazit), it is difficult to determine 

 whether any slight distortion, such as would be induced by bending of the disk, has occurred. It can hardly have 

 been more than a few degrees at the most, since the general direction of the bands is well maintained across the section. 



From the above it is clear that the Algoma iron belongs in the Charlotte group and is in many respects similar 

 to Cohen's Charlotte type which fell in Charlotte, Dixon County, Tenn., in 1835. In all the respects of coarseness 

 of structure, proportions of the members of the triad, varieties of kamacite and plessite, Neumann lines in kamacite, 

 fractures and their fillings, resistance to weathering, Reichenbach's lamellae, and their distribution in the network, 

 it seems to correspond very closely; and one of Brezina and Cohen's plates would fairly well represent the Algoma 

 iron. In composition also there is but slight variation. Both irons are remarkably free from the elements not consti- 

 tuting the triad. Algoma has 10.5 as against 8 per centof nickel; Charlotte has 0. 06 percent of copper, which is not 

 found in Algoma, and the latter has 0.15 per cent of phosphorus, which is absent in the former. 



This meteorite is chiefly preserved at the University of Wisconsin. 



BIBLIOGRAPHY. 



1. 1905: HOBBS. Bull. Geol. Soc. Amer., vol. 14, pp. 97-116. 



ALLEGAN. 



Allegan County, Michigan. 

 Latitude 42 32' N., longitude 85 53' W. 



Stone. Omansite. Omans group of spherical chondrites (Ceo) of Brezina. 

 Fell 8 a. m., July 10, 1899. 

 Weight, 30.45 kgs(70 Ibs.). 



This stony meteorite fell on Thomas Hill, on the Saugatuck Road in Allegan, Michigan, 

 about 8 a. m., July 10, 1899. The main mass of the stone weighed 62.5 pounds and the whole 

 probably weighed not less than 70 pounds. 



According to Mr. Walter Price, as quoted by H. L. Ward, 1 this stone came from the north- 

 west and passed within 40 feet of where he was working, striking the ground about 10 rods 

 beyond, in sand, and burying itself to the depth 'of about a foot and a half. The attention of 

 observers, it is stated, was first attracted by a cannonlike report, followed by a rumbling sound 



