380 



General Description of Lake Erie. 



four feet* in greatest thickness, and extending nearly horizon- 

 tally for 18 or 20 yards, terminates a foot thick. It consists of 

 promiscuously aggregated bundles of crystals united laterally, 

 closely compacted together at the large end of the vein, more 

 loosely in other parts, and having interstices lined with free 

 crystals. The mass is of a white and bluish white colour, im- 

 perfectly translucent. The crystals composing it are from one to 

 four inches long, and from one-fifth to half an inch in breadth. 

 Major Delafield states the cavity in the massive end of the vein 

 to be circular, and three feet in diameter. He found its arch, 

 sides, and floor, to be beautifully studded with pendent crystals, 

 from six ounces to six pounds in weight, and covered Avith a 

 considerable quantity of brown clay and loam. These crys- 

 tals are usually flattened hexahedral prisms. In the Journal 

 of the Philadelphia Academy of Natural Sciences (vol. ii. 

 p. 300) Dr. Gerard Troost has described some of these. He 

 finds their primitive form to be a straight prism, with a rhom- 

 boidal base, of which the angles are 104°, 48', and 75°, 12' (fig. 

 I.) He names a variety of this — ^' Sulphat of strontian trape- 



21 



zienne " AEP (fig. II.) The inclination upon the faces are, of 



* I was at this spot in 1821 for a few minutes in company with Major 

 Delafield ; but, being unexpectedly called away, was prevented from making 

 accurate observations. The dimensions in the text are from Major D. 

 Silliman's Journal, vol. iv. p. 279. 



