TRENTON LIMESTONE. 



297 



y A 



Galena than that of the beds below. Leptwna sericea is a very abun- 

 dant fossil, which has not been observed to be true below. 



Local Descriptions. In the vicinity of Beloit are a number of natural and arti- 

 ficial exposures that are so fortunately situated at different elevations as to exhibit tho 

 entire thickness of the formation, and yet, an equally fortunate cir- 

 FiG. 39. cumstance for the students of geology of that locality, their correct 



correlation is attended with something of difficulty, and is only ac- 

 complished by careful and industrious study. By combining tho 

 partial series shown at the various points, the following general 

 section for that vicinity may be constructed: 



Upper Blub Beds. 



A. A greenish blue hnpure hmestone, chiefly earthy and snb- 

 crystaUine, but in part granular, beds thin and separated with 

 shale, very fossiliferous. Estimated thickness, fifteen feet. 



Upper Buff Beds. 



B. I. In general a fine grained, impure hmestone, of earthy or 

 subcrystaUine texture, the former a Ught bufi,the latter gray, com- 

 bined so as to give an obscure banded and mottled appearance 

 quite peculiar. Nodules of chert are present, which disting-uish 

 it from the rock below. Beds, thick and uniform, fracture, easy and 

 regular iu the upper two-thirds, while that of the lower part 19 

 very rough and angular, as though from a brecoiated structure; 

 more impure than the upper portions. A shaly layer, 7 feet from 

 the base, contains carbonaceous seams with Graptolite markings. 

 Twenty-two feet. 



II. Layer of homogeneous struotm-e, conchoidal fracture, and 

 earthy texture, but sparkling with minute crystals; hned and spot- 

 ted mth obscure reddish fucoidal stains. Two and one half feet. 



III. Combines to some extent the character of the layers above, 

 being less homogeneous than the last, and more so than the pro- 

 ceding. Some layers, very fossiltferous, the remains being grouped 

 more or less in colonies. Horizon of the Halysites. Seven to eight 

 feet;. 



IV. Similar to II, but the characters more marked. Three to 

 four feet. 



v. Similar to I, but not cherty. Texture toward the upper part 

 more irregular than below. Nineteen feet. 



Lower Blue Beds. 



C. Thin-bedded impure limestone of varying earthy and crj's- 



talline texture, interleaved with shaly partings, the whole having 



a bluish-green or gray color. Very fossihferous. Twenty-three 



feet. ^ „ 



Lower Buff Beds. 



D. Thick-bedded, buff limestone, of rather coarse texture, 

 somewhat shaly at the base. Fossils not very abundant except in 

 the shaly portions. Twenty-three feet. 



Transitional layer of sandstone, 2 feet. 

 Transitional layer of impure hmestone, 4 feet. 

 St. Peters sandstone. 



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