THE FLORISSANT LAKE BASIN. 25 



probable from the kaolinized feldspars and the macroscopic fragments of apparently 

 older rocks that the latter are present in the tufa to some extent. This can best be 

 explained by the supposition that it was deposited as a moya or nuulflow within reach 

 of the waters that have worked it over and deposited it in its present position. As we 

 said before, the field evidence must be relied upon mainly in deciding such questions 



as these. 



M, E. Wadsworth. 

 Cambridge, Massachusetts, April 15, 1880. 



Another section, less cavefiilly measured and noted with less detail than 

 the otlier, wah taken at the extremity of one of the promontories jutting in 

 a southwesterly direction into the middle of the upper chain of lakes, alDOUt 

 three kilometers west of the present post-office. The top of the hill was 

 covered with granitic gravel and loose bowlders of dark scoriaceous trachyte; 

 below this we found, passing, as before, from above downward, the following 

 succession: 



SECTION IN THE NORTHWESTERN LAKE. 



{Bii S. II. Sciiddtr and A. Lakes.) 



Decimeters 

 (estimated). 



1. Finely laminated yellow-drab shales; no fossils 12 



2. Coarse decomposing yellowish shales ; no fossils 12 



3. Fine compact drab shales; perfect remains of plants and insects 15 



4. Arenaceous shales; very lignitic 6 



5. Heavily bedded, coarse-grained, crumbling sandstone, of a grayish-yellow and whitish color, be- 



coming ferruginous in places; partially lignitic 60 



6. Chocolate and drab colored shales having a conchoidal fracture, passing below into whitish paper- 



like shales inclosed between coarse arenaceous lamino" ; plants and insects 45 



Total thickness of shales above floor deposits. (Meters, estimated) 15 



These measurements, being estimated, are undoubtedly too great. The 

 composition of this bluff is coarser in character than that of fhe section in 

 the southern extension of the lake. The lignitic beds, which have been 

 used for quarrying purposes, contain numerous fragments of reeds and 

 roots not well preserved. The lower portions of the section correspond 

 better with the other than do the upper beds, where it is difficult to trace 

 any correspondence ; No. 3 of the northwestern seems, however, to corre- 

 spond to No. 16 of the southern series. The whitish paper shales lying at 

 the base of this appear to be entirely absent from the southern section, and 

 the distorted beds which crown the mesa are not apparent in the bluff, or, 

 if present, are wholly regular. A more careful and detailed section of the 

 bluff (for which we had not time), and particularly the tracing of the beds 

 along the wall of the lake, would probably bring to light better correspond- 

 ences. 



