Allen.] 246 [January 21, 



stant, and will require to be definitively settled by the examination 

 of a larger number of specimens than has been possible thus far. 



In concluding, he called attention to the very fine collection of fos- 

 sil Crinoids from the Burlington, Iowa, carboniferous rocks, purchased 

 by the Museum from Mr. Wachsmuth, and of which a part is now on 

 exhibition at the Museum. 



The following papers were read : — 



Metamorphism produced by the burning of Lignite Beds 

 in Dakota and Montana Territories. 1 By J. A. Allen. 



The " Bad Lands " of the Upper Missouri and its tributaries are 

 replete with interest to the geologist and explorer, and though often 

 described in general terms, one of their most important and interest- 

 ing features seems as yet to have been only casually noticed. This 

 is the presence of highly metamorphosed beds of clays and sands, 

 accompanied by pumiceous and lava-like materials, undistinguishable 

 in character from true volcanic products, 2 occurring over an extensive 

 area, remote from any region of true volcanic action ; this metamor- 

 phism being solely the result of the burning out of beds of lignite, 

 and coextensive with the " bad lands " of the so-called Lignite Ter- 

 tiary Formation. 



This formation extends, in the United States, from near the 100th 

 to about the 108th meridian, and from the 43d to beyond the 49th 

 parallel, or over an area of about five hundred miles in an east and 

 west direction and more than three hundred and fifty miles in a 

 north and south direction. Its southern border is, however, quite 

 irregular, being broken into by the Black Hills, between which and 

 the Big Horn Mountains it extends southward as far as the 43d par- 

 allel. To the northward the Lignite Tertiary Formation is said to 

 extend far into the British Possessions, 3 but I have failed to trace 



1 The observations on which the present communication is based, -were made in 

 the summer of 1873, while attached to the North Pacific .Railroad Expedition (Gen. 

 D. S. Stanley commanding) as zoologist of the Expedition. 



2 Specimens of the metamorphosed rocks here described were exhibited to the 

 Society, and have been pronounced by one of our highest authorities, (Dr. T. 

 Sterry Hunt), to be undistinguishable in appearance and composition from true 

 volcanic lavas. 



3 The great Lignite Tertiary Formation is also well-known to extend over por- 

 tions of the valleys of the Saskatchewan and Mackenzie Rivers. 



