490 



L OCAL SECTIONS 



Feet. 



1. Soft, crumbling, white quartzose sandstone, in heavy beds, . . 20 



2. Ash-coloured, argillaceous schistose limestone, with thin marly seams, . 5 



3. Highly fossiliferous shell limestone, of a grayish-blue colour, . . 13 



Both at the Falls of St. Anthony and this place, the fossiliferous beds are sur- 

 mounted by from eleven to twelve feet of drift material, consisting of sand, gravel, 

 and small boulders, on which rests a bed containing Lymnea, Cyclas, Physa, and 

 Planorbis, in great quantities. This I traced for the distance of nearly half a mile 

 on the same level, below the falls. On the trail which leads to St. Paul's, about 

 half a mile from the falls, and elevated from forty to fifty feet above the last-men- 

 tioned deposit, I observed a white marl, highly charged with Lymnea, Cyclas, Pla- 

 norbis, Valvata tricarinata, and other genera of lacustrine and fluviatile shells, such 

 as now live in the neighbouring lakes and streams.* At Fort Snelling, the sand- 

 tone is one hundred and fourteen feet thick ; it is here of a pure white colour, 

 composed of loosely cemented grains of quartz. 



Above this, we have twenty-two feet of fossiliferous limestone, with numerous 

 organic remains, similar to those at the Falls of St. Anthony. The fossils of the 

 upper beds are mostly casts, but the moulds often show the structure of the original 

 surface. Many of the fossils have a coating of sulphuret of iron, which gives them 

 a bright metallic appearance. 



The best section of these rocks that we have observed in Minnesota is at a bluff 

 half a mile below Fort Snelling. The section here is as follows : 



Feet 



1. White sandstone, without fossils, in thick beds, ... 92 



2. Soft argillaceous marlite, of a blue colour, in which no fossils were dis- 



covered, ........ 5 



3. Ash-coloured limestone, clouded with blue, full of fossils. The most 



common are Orthis testudinaria, 0. trkenaria, Leptcena sericea, L. 

 deltoidca, L. planurribona, L. alternata, Terebratula modesta, A. 

 capax, Calymene senaria, Phacops caTMcephdlus, Ceraurus pleu- 

 rexanthemus, Jsotelus gigas. We have also found in this bed por- 

 tions of an Orthoceras, which must have been from two to three 

 feet in length. It has likewise yielded somewhat abundantly a neat 

 little species of Cyiherina, exhibiting a punctate surface, besides 

 several species of Graptolites. These layers effervesce freely with 

 acids, and contain nearly sixty-five per cent, of carbonate of lime ; 

 they will probably afford the best rock for burning into lime of any 



of the beds in the neighbourhood.! Thickness, ... 15 



* See Sect. No. 2, S. 



+ The composition of this rock is as follows : 



Carbonate of lime, ...... 64-85 



" u magnesia, ...... 13-75 



Insoluble matter, ....... 12-40 



Alumina, oxide of iron, and manganese, .... 7'50 



Water, ........ 1-25 



Loss, ........ 0-25 



100 00 



