No abstract

SUMMARY. Equilibrium relations of lead-tin sulphides in the system SnS-PbSnS2 were studied using a sealed silica-tube technique. A complete series of solid solutions forms in the system, and lattice parameters were found to vary lineally with composition. The melting temperature of the solid solution decreases with increasing amount of PbS from herzenbergite at 88o ~ to teaUite at 725 ~ Evidences were found to indicate the existence of this series of solid solution in ore deposits.HERZENBERGITE and teallite are two closely related sulphides of tin, but the equilibrium relationship between them has not been satisfactorily established. Gaudin and Hamlyn (I938) found 'large solubility in the solid state' and no binary compound in the system PbS-SnS. Mosburg et aL 0960, although they successfully synthesized herzenbergite and teallite from elements in sealed evacuated silica-tubes, made no attempt to study the extent of solid solution in the series. Both sulphides were first found in the silver-tin ore deposits in Bolivia. Ramdohr (I935) gave the name herzenbergite to the mineral with the composition SnS, while teallite with the composition PbSnS2 was named by Prior (I9O4). Herzenbergite and teallite are orthorhombic with pronounced tetragonal pseudosymmetry (Hofmann, I935a and I935b), and their cell dimensions are very similar in magnitude as tabulated in table I. Hofmann also pointed out that the crystal structure of the tin sulphides could be related to that of galena. The cell dimension, a (5"93/k), of galena is about half the c of herzenbergite and teallite, and the cube face diagonal [I IO] (4"I9 A) in galena corresponds with a and b of the tin sulphides.Experimental procedures. All syntheses were conducted in sealed evacuated silica tubes. Mixtures of desired compositions were prepared from elements (Fisher certified lead, 99"99 %, Fisher certified tin, 99"95 %, and USP sulphur precipitated). Heat-treatment was done in Nichrome-wound furnaces and temperatures were measured potentiometrically by chromel-alumel thermocouples. Temperature uncertainty was believed to be within • 2 ~ X-ray diffraction was used for the identification of solid phases in the subsolidus region and for the measurement of cell dimensions of the solid solution. Six oscillations were made over the 20 range, 35-55 ~ for each sample of measurement with a General Electric diffractometer. The x Io line of metallic tungsten (from Lamp Metals and Components Department, General Electric Co., Cleveland, Ohio, highly purified) at 20 = 4o.26 ~ (a = 2q648, Swanson and Tatge, 1953) was used as an internal standard. Ni-filtered Cu radiation was used throughout this work. Ore microscopy was used to differentiate the primary solid phases from the secondary solid phases in the determination of the solidus and liquidus of this series.

From the first realization that organic life on this planet has evolved over geologic time, scientists have speculated about the time interval required for these changes to occur. For many years Darwin's idea of slow incremental changes, gradualism, was the accepted model. In the 1970s Stephen Gould (1941-2002) and Niles Eldridge (b. 1943) provided an alternative model of very rapid evolutionary change, followed by long periods of stability, which they called punctuated equilibria. It now appears that Henry Shaler Williams, a geology professor at Cornell University, arrived at the same interpretation almost one hundred years earlier, but only stated this belief in his class lecture notes. He, like Gould and Eldridge, noticed that the fossil record provides evidence that organisms evolved by very fast physical changes occurring in only a few generations and in a very short geological time interval. Then the organisms appear to undergo almost no change for long periods of time; i.e., long periods of stability through many generations. Exactly why Williams did not produce a formal publication of his concept remains a mystery, but his lecture notes from the early 1880s clearly demonstrate that he had developed the idea of punctuated equilibria.

Charles Frederic Hartt was born in Fredericton, New Brunswick, the son of Jarvis William Hartt, a local educator. However, the family moved to Wolfville, Nova Scotia, where young Hartt received his early education, first under the supervision of his father at the Horton Academy and later at Acadia College. Even at the age of 10 or 11, Hartt exhibited a great love for natural history. While a student at Acadia College Hartt's abilities came to the attention of J. William Dawson and under Dawson's guidance Hartt undertook a study of the geology of Nova Scotia. It is reported that Hartt was so excited by his subject that he explored the entire province on foot, from one end to the other. From this field work came Hartt's first paper in which the young geologist disagreed with the ideas of none other than Sir Roderick Murchison with regard to the source of gold in some Nova Scotia rocks. After Hartt's graduation from Acadia College in 1860, the family moved back to New Brunswick, this time to Saint John where his father started a secondary school with Charles as one of the instructors. But Charles was more interested in exploring the region than teaching, and one of his favorite locations was known as "Fern Ledges" on the shore of the Bay of Fundy. In this outcrop of what Dawson identified as Devonian shales (now known to be Pennsylvanian Age), Hartt discovered what were the oldest known insects of the time. This and his other work brought him to the attention of Louis Agassiz and led to an invitation to study at the Museum of Comparative Zoology at Cambridge, Massachusetts. Even after he went to study with Agassiz, Hartt continued to work in New Brunswick and Nova Scotia during the summers, culminating in the summer of 1864 when he was employed with George F. Matthew, Professors L. W. Bailey, and Dawson to do a geology survey of New Brunswick. Hartt left his homeland soon afterward and turned his geological prowess on Brazil, but only after he had learned his craft walking over the hills and valleys of the Atlantic Provinces.

No abstract

No abstract

No abstract

No abstract