MATERIAL FROM DKVIL 111 I.I. IBO 



j)ortii)ii ol" ii j^reiit l)i}>e on Devil ilill. Kx})oscil lor a. (lislaucc of about 

 UK) yards, this giant pipe is iiiade up of sand crystals throu<^bout its 

 extent. Below may be seen innumerable small sand crystals, and in 

 front a small pipe bristling wilb concretion crystals. The length of this 

 remnant of a bed, which from its coarseness suggests a current dej)osit, 

 is probably 500 yards in all, and it scarcely measures 20 yards at its 

 widest point. In this band the material varies slightly, running from 

 sand into gravel at times. 



Overlying the crystal bed occurs some 25 feet of conspicuously cross- 

 bedded and fairly coherent sand rock with ragged outline. 



In the loose underlying cr3'stal bed the sand is finel}' laminated, ex- 

 hibiting colors as contrasting at times as black and white. The lamime 

 extend uninterruptedly through sand, sand crystals, concretions, and 

 pipes. All the cr3^stals show laminated lines. Planes of weakness fol- 

 low the laminae, and two effects are produced : first, the crystal, if ex- 

 posed to atmospheric action, weathers more readily along certain planes, 

 leaving others projecting; second, the crystals break more readil}"" along 

 certain lines (see plate 18, figures 1 to 9). This fracture is but a i)art- 

 ing along the bedding plane, and is not to be confounded with cleavage, 

 however like it it may appear. Although cleavage lines are present in 

 the calcite, the sand, which is the predominating element, interferes with 

 the cleavage throughout the mass, though mau}^ crystals imitate the 

 calcite angle in fracture. 



The most interesting single feature connected with these crystals seems 

 to be the wonderful transition from the solitary crystals to the concre- 

 tions, compound concretions or pipes, to the compound pipes and solid 

 rock. This takes us back to the radiating concretions and compound 

 concretions seen in our western counties, especially in Sioux county. It 

 was this intimate relation between the sand-lime crystals and at least one 

 type of concretionary structure which suggested the name concretion 

 crystals. However, sand crystals or sand-lime crystals, as first proposed 

 by the writer in 1893, seem to be simpler and more expressive terms, in- 

 asmuch as they explain the composition. These have subsequently been 

 described b}^ Penfield and Ford in the American Journal of Science of 

 May, 1900. 



Immersed in acid, the crystals are quickly broken down, the calcite 

 being dissolved and the sand grains liberated. 



To the observer in the field, it is interesting to note how these crystals 

 var}^ from yard to yard in the same bed. Thus they pass through all gra- 

 dations of size — from those scarcely a quarter of an inch (6 millimeters) 

 long to those exceeding 15 inches (38 centimeters) in length, the average 

 size, of which there are myriads, being 22 to 3 inches (6 to 8 centimeters). 



