104 Disoorerfj of Lanfuia and Punfdo.ridf^H — D'hicht//, 



their description of pipes made from it. But these white spot?? 

 are wholly distinct from those. These are formed by the merest^ 

 most volatile, thin scale, which in the weather seems to disappear 

 soon. On Scraping ofE a quantity of the stone containing these 

 thin scales, they are found to contain a trace of phosphoric acid, 

 though consisting largely of carbonate of lime. These little shells 

 are about a quarter of an inch in diameter, and one valve some- 

 times- seems to have a beak that projects sliglitly more than the 

 other, indicating the genus L/y/;(/?/7a rather than iJischui. There 

 is on some of the impressions a faint sub-central protuberance 

 which at first I thought indicated Diar'nut^ but this seems not con- 

 stant in position nor in form, and is not surrounded by any concen^ 

 trie striation or other structure. 



A short time after finding these impressions Mr. A. W. Bar- 

 ber of Yankton, Dak., sent me another supposed fossil found by 

 him at the same place and in the same beds. It h^s the form of a 

 distorted and folded trilobite, from which the anterior portion, and 

 the testaceous covering of the whole animal is wanting. The tri- 

 lobed structure is made more evident by sup])0sing the left lateral 

 lobe is turned under the animal and folded u[)on itself. The 

 ridges and furrows formed by the folded segments of the left lobe 

 are plainly seen on the under side of the animal running trans- 

 verse to those on the upper side. This seems to be a species of 

 Pamdox'tdes^ and points to the horizon of the St. .Johns' group as 

 the probable equivalent of these red quartzites. 



The simple discovery of fossil remains in these i-ed quart/ites 

 would not be of sufficient importance to warrant any special notice 

 had not the age of these strata been a subject of some difference 

 of opinion among the geologists of the northwest, and had not 

 the organic nature of these impressions 1)een d()nl)ted l\y some to 

 whom they have been shown. 



It is not necessary here to enter into the detailed history of 

 opinion and investigation respecting the age of these rocks. 

 They have been classed as Huronian, as Archiean, and as Potsdam. 

 They are extended over a wide belt in southwestern Minnesota. 

 At New Ulm they are separated by a quartzose pebbly conglomer- 

 ate from a coarse red granite. At several places in Wisconsin 

 they are associated with red felsite and ])orphyry, and become 

 gneissic, and in the same manner they have been assigned to differ- 

 ent ages. Red quartzites and gneisses, and red felsites and por- 



