THE NONMETALLIC MINERALS. 261 



Aside from the locality at Helgustadir, calc-spar in quantit}^ and 

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

 in West Iceland. 



The Reydharf jordhr locality was also visited by Mr. .7, L. Hoskyns- 

 Al)rahall in the suniuier and autumn of 1880, and whose jiccount^ is 

 reproduced in part IjoIow. 



Sudhrmula Sysla, of which lieydharf 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 hig-h. This has ])een sul)sequently eroded into sharp, bare 

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

 bv 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 b}^ 5 yards and some 10 feet high, originally filled almost 

 entir(dy, 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 Syslumadhur," 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 w^alking 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 w^hich the cave is formed is a dolerite, and darker in color than 

 the surrounding- phonolite, which is traversed by veins of Idack and 

 green pitchstone. In the neighboi'hood of the spar it is disintegrated, 

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

 stilbite and calcite. 



The quarry was worked till 1872 l)y 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 da3''s 



' ]Mineralogical Magazine, IX, 1890, p. 179. 



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



