OGLE COUXTY. 115 



The Buff Limestone. The lower division of the Trenton, or the Buff 

 limestone of Owen, next succeeds in the descending order. It crops out 

 in many places in close proximity to the St. Peter's sandstone. In some 

 places it is separated from the overlaying division by a few feet of shale 

 and blue clay ; in others the transition from the one to the other is not 

 easily distinguished. In the former, it is thick-bedded, compact, and the 

 heavy layers are divided by thin fossiliferous layers and thin blue bauds 

 of clay ; in the latter it is shaly, shingly, yellowish buff-colored, re- 

 sembling much certain parts of the Blue division. 



Dr. EVERETT'S description of this rock corresponds with my own obser- 

 vations, so far as outcrops in close proximity to the St. Peter's sandstone 

 were examined. In the ravines above and opposite Oregon ; at Sharp's 

 mill, on Pine creek: at Moore's quarry, in Lee county; on Kite river, 

 and in one or two other places, this is true. At Sharp's mill and near 

 Oregon, the lower layers are of a dull earthy color and fracture, with 

 considerable sand in their composition, and on being struck with the 

 hammer, give a heavy dead sound or thud, as if striking a mass of 

 frozen earth. 



This description would hardly apply, however, to the outcrop at 

 Byron. This corresponds exactly with WHITNEY'S description of the 

 Buff limestone outcrops at Wiuslow and Beloit; and these are exactly 

 like many outcrops of the Blue division, except that the fossils do not 

 seem to be identical. 



Fox*!!*. At Moore's farm, in Lee county, many fossils were observed, 

 mostly imperfect casts on the thin layers of shaly matter, separating 

 the massive layers, and also on the surface of some of the massive 

 layers. But in the Ogle county outcrops we could hardly detect a fos- 

 sil, except at Byron. There we found a part of a large Orthoceras, six 

 inches in diameter, perhaps. The animal to which it belonged must 

 have been six or seven feet long. 



Tli e St. Peter' 1 s Sandstone . 



This very interesting formation outcrops heavily in this county. It 

 is the prevailing rock along Kock river, from about two and one-half 

 miles above Oregon to three miles below Grand De Tour, a distance of 

 about fifteen and one-half miles. Where the bluffs and high land come 

 up to the river this rock nowhere outcrops more than a mile or two back 

 from the stream. Even the river bluffs, along the sandstone region, if 

 places, are capped by the limestones of the upper Blue and Buff. But 

 iip the tributary streams low outcrops may be noticed extending miles 

 back from Eock river. Up Pine creek it may be traced as high as 

 Sharp's mill, some five miles from the river. Up Kite river, for per- 



