No. 5.] DAWSON — LIGNITE FORMATIONS. 24^ 



miles west of Rod lliver, and the cliief exposure is sotnethinj^ 

 less than a mile south of the line, and in the Territory of Mon- 

 tana. A seam of ligniLC coal no less than 18 feet thick there 

 crops out. The section, including this liyuite, is as follows, iik 

 descending order : 



1. Siiif'iut' soil 1 foot in. 



2. Drift (quartzitf pi'bhles) 1 " 6 



3. Yoliowisli and gwy stratiiicd «au(ly 



clays 9 " 



4. LiKiiiU! " 9 



5. Uiown, handed clays, with plants and 



some rrystalliiu! gy[)sum 5 " 



G, Lignitt; (weatlicring soft) 10 " 



7. liiguitt; (hard and compact) 8 " 



8. Soft grey sandstone 5 " 



40 3 



The laminated clays of bed 5 when first exposed show plant 

 remains in great perfection ; even the delicate fronds of ferns^ 

 which are here unusually common, showing every detail of their 

 form. On drying, however, the clay becomes cracked and fis- 

 sured, and it is with difficulty that the impressions can be pre- 

 served. The association of selenite crystals, isolated or in groups,. 

 with the clays and arenaceous clays holding plant remains, is 

 very constant. 



The upper part of the lignite bed weathers soft and forms a 

 steep slope. The lower part is hard, and being divided by ver- 

 tical jointage planes, like many true coals, falls into the stream 

 in great rectangular blocks, and presents a vertical face. 



The plants associated with the lignite beds are very numerous 

 in species, but have not yet been fully examined. Many Jiag 

 and sedgc-Wke leaves occur. At least two kinds of Ferns are 

 represented — a Sphvnopteris and an Onoclca apparently identi- 

 cal with 0. seiisihilis, a form still living. There are also twig» 

 of several coniferous trees, including a cedar, TIhiJk interrupta 

 of Newberry, and apparently species of Seipmla and Tuxns ;■ 

 and from the microscopic structure of the lignites it would 

 appear that most of them are made up of woods of this kind. 

 Leaves of a great many species of deciduous trees also occur, and 

 are generally full grown, and appear to have fallen in the order 

 of nature, and at the change of the season, and floated quietly 

 out into the great lakes, in the fine silty deposits of which they 

 have been preserved. Fopulus, ^nlix, Ulmus, Plutanus, and. 



