A. A. Young — Sands of the Potsdam Sandstone. 47 



Art. V.— Further observations on the Crystallized Sands of the 

 Potsdam Sandstone of Wisconsin; by Eev. A. A. Young-. 



A BRIEF note on the on stallixrd sands of the Potsdam sand- 

 stone quarried at New Lisbon and the St Peter's sandstone of 

 Wisconsin is published on page 257 of the last volume of this 

 Journal. A fuller account of the observations which I have 

 made is here given. 



The quarries near New Lisbon affording the sands described 

 are situated five miles north of the place. The rock is a hard, 

 compact and mainly very line-grained sandstone. Some slabs 

 carry excellent ripple-marks ami fossil tracks. The rock 

 sparkles brilliantly in the sunlight through the reflection from 

 innumerable but minute faces of crystals. When broken up 

 and prepared for the microscope, nearly all the grains show, at 

 least on some part of tin it surface, a > >rtion of ;u edge, or face, 

 or an apex of a crystal. 



The most finished crystals occur 



whicbT are only -004 in. X -0035 in. in 

 longer and shorter axes. Much of the 

 ^ sand varies from .=*,- to T J f - of an inch 



• ^ in longer diameter. Some of the small 

 X grains are complete in their crystalline 

 _U-^<7 form, save at some spot of detachment 

 / from a neighboring grain. The sim- 

 plest form is that of the double six- 

 sided pyramid, but others have por- 

 \[/ tions of the intermediate prism of vary- 



ing lengths ; and besides these are oth- 

 ers with modifying planes. A frequent form is roughly pear- 

 shaped, carrying at the smaller end "a point of a pyramid, and 

 at the larger a cluster of minuter pyramids. The larger part 

 of the grains have many irregularities of form, whose explana- 

 tion is obvious when the sand is mounted in balsam. 



Accompanying the sand 'are certain brown kidney-shaped 

 grains, •<><>:} in. in diameter and smaller, smooth for the most 

 part, which closely resemble certain enclosures that arc found 

 in the grains of sand. The rough exterior of part of the grains 

 appears to have sometimes come from the breaking apart of 

 cohering grains. Some of these rough spots occur in the midst 

 of smooth faces, and are shallow six-sided pits with straight 



While dry mounting exhibits to the best advantage the crys- 

 -. a balsam mounting, or its i 

 best the interior structure and the mode of origin. Thus 



