THE NONMETALLIC MINERALS. 261 



Aside from the locality at Helgustadir, calc-spar in quantity and 

 quality for optical purposes is known to occur only at Djupifjordur, 

 in West Iceland. 



The Reydharf jordhr localh"y was also visited by Mr. J. L. Hoskyns- 

 Abrahall in the summer and autumn of 1889, and whose account 1 is 

 reproduced in part below. 



Sudhrmula Sysla, of which Reydharf jordhr, the largest, bisects the 

 east coast of Iceland, are cut out of an immense plateau, formed of 

 horizontal sheets of volcanic rock, chiefly trachyte, between 3,000 and 

 4,000 feet high. This has been subsequently eroded into sharp, bare 

 ridges with immense cliffs or steep slopes falling from them, parted 

 by torrent valleys and fjords, the greater part of the district not reach- 

 ing the present snow line. It is on one of these slopes, which slants 

 down at an angle of forty degrees into Reydharf jordhr, that the unique 

 quarry of Iceland spar is found. It consists of a cavity in the rock 

 about 12 by 5 yards and some 10 feet high, originally filled almost 

 entirely, but now only lined, with immense crystals, which are fitted so 

 closely together as to form a compact mass, like a lump of sugar, with 

 grains averaging 10 inches across. % 



The Syslurnadhur, 2 Jon Asmundarson Johnsen, had given me leave 

 to examine the cave and take as many specimens as I liked, but the 

 permission was not of very much use, there being about 5 feet of 

 water nearly all over the bottom; and such specimens as 1 did get 

 involved doing severe penance in walking barefoot over sharp crystals. 

 The floor is covered with a thin layer of very fine chocolate-brown mud, 

 which sticks as tenaciously to one's feet as to the crystals. I had to 

 resort to tooth powder to get the latter clean, though the great heaps 

 of spar which lie on the path side and in front of the mouth of the 

 cave were all washed by the rain till they were as bright and trans- 

 parent as ice. The water now running through the cave is incapable 

 of forming calc-spar. It appears, like the surrounding rocks, to con- 

 tain an excess of silicic acid, and either etches the surface of the spar 

 wherever it comes in contact with it, or covers it with stilbite, the 

 characteristic zeolite of the doleritic and basaltic rocks in Iceland. The 

 rock in which the cave is formed is a dolerite, and darker in color than 

 the surrounding phonolite, which is traversed by veins of black and 

 green pitchstone. In the neighborhood df the spar it is disintegrated, 

 colored slightly with green earth, and full of microscopic crystals of 

 stilbite and calcite. 



The quany was worked till 1872 by Herra Tulinius, a Danish mer 

 chant of Eskif jordhr. The trading station is an hour and a half's ride 

 from Helgastadhir, the nearest farm to the quarry. (In Iceland all 

 distances are measured in terms of the hour's ride, tima, and the day's 



1 Mineralogical Magazine, IX, 1890, p. 179. 



2 Magistrate, public notary, receiver of taxes, liquidator, auctioneer, etc. 



