2S8 GEOLOGY OF EASTERN WISCONSIN. 



the calcareous layers of tlie Trenton, for several feet above their base. 

 At most other points the iisual abrupt transition was observed. 



Organic Bemains. Previous to the present year (1876) there has 

 been no published announcement of the existence of fossils in this 

 formation. In the Fourth Annual Eeport of the Geological Survey 

 of Minnesota, Prof. JST. H. Winchell describes a Lingulepis, found 

 near Fountain in that state, in the upper beds of the formation. 



In my unpublished report of 1873, Scolithus borings were de- 

 scribed as occurring in rock in the town of Waterloo, referred to the 

 St. Peters sandstone. In 1874, this was confirmed by finding well 

 preserved tubes of the same in the town of Beloit, in strata belonging 

 to the upper part of the formation. Fucoidal impressions were also 

 found at the same locality. In 1875, Scolithus tubes were seen iu 

 sandstone referred doubtfully to the base of the formation. 



In a synopsis of my report for these years, three hundred copies of 

 which were printed and distributed at private expense, in the early 

 part of January, 1876, the existence of organic remains in this for- 

 mation was announced. This form of announcement will not proba- 

 bly be regarded as sufficient to justify a claim to priority, in this in- 

 teresting discovery. The organic remains so far have been found ex- 

 clusively where the sandstone was compacted by some cementing ma- 

 terial, which justifies the belief that the absence of fossils throughout 

 the greater part of the formation is due to want of preservation and 

 not to original absence of life in the depositing sea. 



Method of formation. The existence of the remains of marine 

 life demonstrates that the fossiliferous portions at least are submarine 

 deposits, -while the well rounded character of the grains, the ebb and 

 flow structure, the shaly laminations, the conglomeritic portions and 

 its relations to the adjacent formations leave no doubt that it belongs 

 to the common class of oceanic sand deposits. 



Extent and Local Descriptions. The St. Peters sandstone enters this district from 

 niinois and from the Lead Region at the southwestern corner of Rock county. Owing 

 to the ease with which the sandstone is eroded, it usually occupies only a narrow belt 

 close under the protecting ledges of the overlying Trenton Kmestone, and appears on 

 the map as a narrow border to that formation. In some places, as in Rock county, 

 where it is represented as occupying more ample areas, it is quite probable that if the 

 drift could be removed the sandstone would be found absent at some points. The pre- 

 glacial rivers undoubtedly cut entirely through it, but their position cannot now be ac- 

 curately mapped. 



In Rock county it may be readily identified, since it seldom shows itself except under 

 a protecting shelf or crown of Trenton limestone, whose characteristic fossils are easily 

 recognized, and by the simpler fact, that it is the only sandstone exposed in the county. 

 Its upper portion is amply displayed in the western portion of the county, where the 

 drift is light, but presents so great similarity that it will be unnecessary to enter into 



