352 HALL AND SARDESON — PALEOZOIC FORMATIONS OF MINNESOTA. 



noted nor a mixture of dolomitic pebbles torn from the underlying Mag- 

 nesian. as is the cast' in Wisconsin* Tiro outliers of this sandstone at 

 Chimney rock, in Marshan township, and at Castle rock, both in Dakota 

 county, show sonic strong color markings due to infiltration, and they 

 show strong cross-bedding and in places a distinct lamination. The dif- 

 ferent degrees of hardness of the layers induce the interesting sculpturing 

 which gives name to these exposures, whose existence is doubtless due 

 to the presence until recently of a cap of Trenton limestone. 



Paleontologic Characters. — The fauna of the Saint Peter has until re- 

 cently been almost unknown. In Wisconsin in 1873 and 1874 Cham- 

 berlin found scolithus tubes and fucoidal impressions f at Beloit and 

 Waterloo. In 1875 N. If. Winchell found IAnguhpis morsensisX (which 

 name was subsequently changed to Lingula morsei by S. A. Miller;; and 

 in 1884 X. PI. Winchell also recorded the presence of circular pits in the 

 sandstone at Faribault and Castle rock.§ The writers also have noted 

 these borings, and on exploring them have found larva' casts ; moreover. 

 these tubular markings have not been noted in fresh deep exposures ; 

 hence the fossil nature of the borings is regarded with some suspicion. 

 < me year ago one of the writers discovered quite a number of fossils in 

 a small railway cut near Highland park, on the Chicago, Burlington and 

 Northern railway, a few miles from Saint Paul; these fossils comprised 

 several genera and species already recognized. || During the present 

 month (December), at a cut between the Chicago, Saint Paul and Kansas 

 City railway shops and south Saint Paul, fossils were found in large 

 numbers, all comprised, however, in three or four species. The sand- 

 stone in which these last fossils were found is almost pure white. Chem- 

 ically it is nearly pure silica. It was this fossiliferous rock that Mr. 

 Hortvet analyzed with the result given on a preceding page. In both 

 localities the shells are wholly absorbed. At Highland park a stain of 

 ferric oxide covers the walls of the casts; yet the growth markings are 

 distinct. Near south Saint Paul the walls are perfectly smooth and show 

 distinctly muscle impressions, as well as growth striae. These markings 

 are easily obliterated with careless handling, owing to the extreme fria- 

 bility of the rock. The study of this newly discovered fauna is in prog- 

 ress : yet enough is already known to show that it is thus far almost wholly 

 molluscan. Murchisonia gracilis, Hall, M. perangidaia, Hall, with four 



other gasteropods ; two new species of Modiolopsis ; Tellinomya, sp. undet. : 



. 



* Charoberlin : Geology of Wisconsin, vol. ii, 1*77, p. 287. 



j If »id.. p. 288 



I Geological and Natural History Survey of Minnesota, Ann Rep. for 1875, p. 41. 



ogy of Minnesota, Final Report, vol i. 1884, p. 656. 

 || F. W. Sardeson : Fossils in 1 he Saint Peter Sandstone. Bull. Minn. Acad Nat Sci., vol. iii, no. ::, 

 1892, p. 318. 



