234 Field Columbian Museum — Geology, Vol. i. 



Type 2. — Crystals of this type are characterized, as has been said, 

 by an amber yellow color. This may be deeper or paler. The size 

 of the crystals is also remarkable. Some are known 2^ feet (.76 

 meters) in length, and the average size of those seen in collections is 

 from 6 inches (.15 meters) to 1 foot (.30 meters) in length. Those 

 seen in collections are rarely, if ever, doubly terminated, only about 

 half of the complete crystal being present. Some account of the 

 mode of occurrence of these crystals in a cave as well as a plan of 

 the cave is given, as already mentioned, on p. 567 of Vol. vii, 

 Reports of the Missouri Geological Survey. For the following fur- 

 ther information I am indebted to Mr. Henry Weyman, the present 

 owner of the cave : " The cave is from 250 to 300 feet long, from 40 

 to 60 feet wide and of an unknown depth in places, i. e., we have 

 never been able to measure the bottom, as only a part of it is above 

 water. The whole opening is covered with crystals of various sizes, 

 leaving no place on any of the roof or wall exposed and going down 

 as far as can be seen in the water. At one place a slab covered with 

 large crystals has fallen from the roof at some time, and since then 

 new crystals have formed on the roof where the slab has been broken 

 away; also new crystals have formed on the broken side of the slab 

 after it had fallen down. The largest crystals, I should think, would 

 measure 2 to 2^ feet long. The greater part of the crystals are 

 doubly terminated, ending in very sharp points. The cave was dis- 

 covered by mining after lead and zinc ore, when a shot put in the 

 bottom of the drift broke through the roof of the cave and so exposed 

 the mass of beautiful crystals. This is so far the only opening allow- 

 ing admittance to the cave. It is our intention to preserve the cave 

 in its present state and make access to it more convenient to visitors." 

 It is also stated in the account previously mentioned* that the cave 

 is remarkable for the entire absence of stalactites of the usual type. 

 Since these are absent it is probable that the cave at the time of for- 

 mation of the crystals was filled with water holding carbonate of lime 

 in solution, from which crystallization took place. Had the cave 

 been only in part filled with water, the dripping waters would doubt- 

 less have formed stalactites of the usual type. 



The form of the crystals of Type 2 is primarily determined by 

 the common scalenohedron v, -\- R3. This may alone constitute the 

 crystal or its form may be slightly or highly modified. A common 

 modification is the truncation of the apex of the scalenohedron by the 

 rhombohedron <?,-^ R. Fig. 2, PL xxviii, represents a combination 



♦Report of the Missouri Survey ioc. cit. 



