CHALK 



1260 



CHALLENGER EXPEDITION 



him to begin a new life in the land of Canaan 

 (Genesis XI, 31). It is supposed that the 

 Chaldeans were a Semitic people who came 

 from Arabia at a very early date and settled 

 in the neighborhood of Ur. From there they 

 began to make war upon the other inhabitants 

 of Babylonia, and at various periods Chaldean 

 princes sat upon the Babylonian throne. 

 About 626 B. c. Nabopolassar founded the Chal- 

 dean (or New Babylonian) Empire, and he and 

 his famous son, Nebuchadnezzar, made Bab}'- 

 lonia a world power. 



The last Chaldean king ruled about 556 B. c., 

 but during this period the union between the 

 Babylonians and Chaldeans had become so 

 complete that in later history the terms Chal- 

 dean and Babylonian are used without distinc- 

 tion between the two. In the book of Daniel 

 Chaldean is applied not only to the Baby- 

 lonian people but to a class of magicians. See 

 BABYLONIA. 



CHALK, chawk. The mark made on the 

 blackboard with white crayon contains mil- 

 lions of fragments of the shells of tiny creatures 

 which ages and ages ago lived on the bottom 

 of the sea. As these little animals died they 



CHALK 



left thin skeletons which in the course of ages 

 turned to a soft, white limestone that we know 

 as chalk. 



When seen through the microscope, a piece 

 of chalk shows hundreds of these tiny shells 

 of different forms and sizes. Some resemble 

 snail shells; others are circular and beautifully 

 marked, while others resemble needles. The 

 needle-like objects came from sponges. Chalk, 

 then, is nearly pure limestone, composed 

 almost entirely of these shells. 



The great white cliffs in France and England 

 on each side of the Strait of Dover are com- 

 posed of chalk, and the cliffs on the English 

 side gave the name of "Albion" to England 

 centuries ago, for Albion is believed to have 

 been derived from Gaelic words meaning white 

 and hill. There are extensive beds of chalk 

 also under the city of London. In the United 



States it is found in Arkansas, Texas, Iowa, 

 Montana and a few other states. Some of the 

 beds are over 600 feet thick, so the period 

 during which the chalk was forming must have 

 been very long (see CRETACEOUS SYSTEM). 



Uses. The use with which we are most fa- 

 miliar is for marking on blackboards. The 

 crayons are made by grinding the chalk, mixing 

 the powder with some substance which will 

 hold it together, and shaping the paste in 

 molds. For this reason if crayon dust be 

 examined with the microscope no fragments of 

 shells may be found. When ground and mixed 

 with water chalk forms a whitewash; whiting 

 is ground chalk from which the grit has been 

 removed. In both England and America chalk 

 is used to some extent in the manufacture of 

 cement (which see). As a rock it is of no 

 value for building purposes, because it is easily 

 crushed. 



CHAL'LENER, FREDERICK SPROSTON (1869- 

 ), a Canadian painter, noted for his land- 

 scapes and mural decorations. Though born 

 and educated in England, he has made Canada 

 his home since 1883. He studied at the On- 

 tario School of Art, and also in Italy, Egypt 

 and Syria. He is a member of the Ontario 

 Society of Artists and of the Royal Canadian 

 Academy of Art. Among his best pictures 

 are Workers of the Fields and A Song at 

 Twilight (both in the National Gallery, Ot- 

 tawa), When the Lights Are Low a*nd A Quiet 

 Old Road (in the Provincial Art Gallery, To- 

 ronto). Equally famous are his mural paint- 

 ings in the Russell Theater, Ottawa; the King 

 Edward Hotel, Toronto; the Royal Alexandra 

 Hotel, Winnipeg, and the Hotel Macdonald, 

 Edmonton. 



CHALLENGER EXPEDITION. One of the 

 greatest journeys of purely scientific investiga- 

 tion for studying the conditions of the oceans, 

 and the one most fruitful in results, was the 

 undertaking known as the "Challenger Expedi- 

 tion." At the suggestion of the Royal Society 

 of London the British government fitted out 

 the ship Challenger, of 2,300 tons, for a long 

 cruise around the world. The vessel sailed 

 from Portsmouth, England, in December, 1872, 

 and did not return to England until May, 

 1876. During the four years the Challenger 

 cruised in all directions in the Atlantic, South- 

 ern and Pacific oceans, traveling nearly 68,000 

 nautical miles and making investigations at 

 362 stations. 



During the journey deep-sea soundings were 

 continually made; samples of water at various 



