240 [May, 1845. 



tance from the Fort of about half-a-mile, that gentleman had a view of the 

 horizontal outcrop of the lands of rock through a height of about 80 feet, com- 

 mencing 80 or 100 feet above the river, and terminating more than 100 feet be- 

 low the general level of the rolling plains, which are here nearly 300 above the 

 bed of the Missouri. The section which he constructed was subsequently lost. 

 It exhibited 15 different beds of alternating soft clays, uncemented sands, and 

 soft argillaceous sandstone. 



In the upper part of this section occurs lignite, some of which is in the con- 

 dition of a very friable charcoal. 



The fourth and fifth, layers in this section are especially interesting. The 

 4th is a bed of clay, the 5th a layer not more than one foot in thickness, of a 

 brown ferruginous argillaceous rock. They contain three or four species of 

 freshwater univalve shells, Lymnea, Planorbis, &c. One of the species of 

 Planorbis it is conjectured may be a form now extinct, but the mutilated con 

 dition of the specimens prohibits a positive opinion. 



Within one mile and-a-half of the locality of the section just alluded to, there 

 is a stratum of fine-grained argillaceous sandstone of a light-grey colour, with 

 minute black specks. This occupies a higher level than the top of the section. 

 The rock is exposed in a quarry through a thickness of 20 or 30 feet, whence 

 building stone has been procured for the foundations of the fort. Like the beds 

 previously described, this stratum furnishes proof of a freshwater origin. Among 

 the specimens from it, is one presenting the two valves of a bivalve shell, appa- 

 rently an Anadonta ? 



It also contains leaves of deciduous trees, bearing a close resemblance to those 

 of the Beach. Besides these indications we have evidences derived from the 

 remains of what was probably a mammiferous animal. Two fragments of bone 

 procured at one of the above localities, indicate by their cancellated structure an 

 animal of this type ; but they were too imperfect to enable us to decide the 

 order to which they belong. 



The proofs thus afforded of a probably widely diffused freshwater formation 

 in the region of the Upper Missouri, reposing upon the cretaceous strata, and 

 imbedding remains of a manifestly tertiary age, are just at this time invested 

 with considerable interest, from their according with the discoveries recently 

 made by Captain Freemont, of the presence of other and probably extensive 

 freshwater tertiary strata in the Oregon Territory. \ 



All which your Committee beg leave respectfully to Report. 



Henry D. Rogers, 

 S. G. Morton, 

 Walter R. Johnson. 

 Philadelphia, May 15th, 1845. 



