NATURAL SCIENCES OF PHILADELPHIA. 109 



back it out again, owing to the resistance of tlie branches on the ground and of 

 other bushes, so, like the sailor who throws overboard a portion of iiis cargo to 

 enable him to save the rest, thej' cut oflF this piece that they might steer clear 

 of the difficulty with the remnant of their treasure. The chips are from the 

 larger specimen ; in cutting them out they must work horizontally around the 

 trunk, and when they have cut two grooves at the proper distance apart, they 

 take hold of the isolated portion with their teeth, and split off portions vertically, 

 and so in succession split off chips until they have girdled the tree ; a second 

 course is then removed from the bottom of this, and so on diminishing the size 

 of the chips until the tree is only supported by a portion of its heart connecting 

 the apices of two cones — one on the stump upright, the other on the butt of the 

 log inverted. In this manner, also, the Indians cut down trees with their 

 hatchets, leaving the same form of a cone on the but of the log and on the stump, 

 as their beaver neighbors have done before them. 



3Iay 2QtJi. 

 Mr. S. Ashmead in the Chair. 



The Committees to whom were referred the following papers, reported 

 in favor of their publication : 



" Notes Explanatory of a Map and Section illustrating the geological 

 structure of the country bordering on the Missouri River, from the 

 mouth of Platte River to Fort Benton, in lat. 47" 30' N., long. 110^ 

 30' W., by F. V. Hayden, M. D." 



" Explorations under the War Department : Description of new Cre- 

 taceous and Tertiary Fossils collected by Dr. F. V. Hayden in Nebraska, 

 under the direction of Lieut. Gr. K. Warren, U. S. Top. Engineer, 

 with some remarks on the geology of the Upper Missouri country ; by 

 F. B. Meek and Dr. F. V. Hayden." 



"On the Larva of Thyreus Abbotii, by J. P. Kirtland, M. D." 



Explorations under the War Department. 



Notes Explanatory of a Map and Section Illustrating the Geological structure 

 of the country bordering on the Missouri River, from the mouth of the Platte 

 River to Fort Benton, in lat. 47° 30' N., long. 110" 30' W. 



BY P. V. HAYDEN, M. D. 



(Communicated hy permission of the Secretary of War.) 



The facts from which the accompanying map and section have been con- 

 structed, are mainly the results of three years' explorations by me in the north 

 west;* and although some of them have heretofore been given to the public 

 in brief written accounts of the geology of that country,f this is the first time 

 they have been presented in this form. 



In regard to the Map, I would simply state that it is based on the most re- 

 cent topographical explorations. The geology, however, is of course not 



* The geology of portions of north-eastern Kansas has been colored on this 

 map from information kindly furnished by Maj. F. Hawn, of Weston, Missouri, 

 U. S. Dep. Surveyor in that region. 



For the information respecting the geology of Platte Paver valley, I am in- 

 debted to Mr. Henry Pratten of the Geological Survey of Illinois. 



t See several papers by Mr. Meek and the writer in 8th vol. Proceed. Acad. 

 Nat. Sci., Philada. 



1857.] 



