RARRIS OUR LOCAL GEOLOGY. 21 



situated on the brow of the bluff facing the river, and shows the fol- 

 lowing section: 



° FEET. 



1. The uppermost member is a fine-grained limestone wnth few 



fossils, layers growing thinner towards the base. ... 5 



2. Encrinal limestone resolvable into three layers, the upper part 



of each crowded with, the lower more sparing, of fossils. 6 



3. Thin shaly limestone abounding in bryozoa and corals, brach- 



iopods generally crushed and massed together, Orthis being 

 the most prominent 5 



Beginning at this quarry and still going westward, within the next 

 four miles is found, at comparatively short distances from each other, 

 no less than six long ravines, each, in its course, contributing some- 

 thing to our knowledge of the rock. This whole ravine region de- 

 serves a slight notice. I have called them ravines. In reality they are 

 valleys of erosion two or three hundred feet broad, thirty to fifty feet 

 high, not the result of any forces now^ in existence. The little streams 

 have simply hunted them up — taken advantage of their work to make 

 the nearest way to the river, doing some excellent work as they passed 

 along. Their apparent origin seems simple. Little rivulets originat- 

 ing back in the prairies running southward, swollen by rains and es- 

 pecially spring freshets, have cut their way through the soil and into 

 the upper part of the shales, have ploughed deeper in their course as 

 they approach the bluff, leaving on their banks for a mile or more 

 masses of rock and shale. The excavation goes on through the long 

 slope stretching towards the river, building a channel for its course. 

 The rock, whether exposed in the ravines, at the bluff, or on the long 

 slopes extending to the river, with one exception, is always that of the 

 Spirifer Pennatus beds. All the quarries that have been opened are 

 in the same beds. Along the crown of the slope occur their most 

 prominent features. 



A few rods east of Mr. Sauer's quarry and along its side extends 

 the First Ravine. Though shorter than some of its neighbors, it 

 originates back in the prairie, and along its course for a long dis- 

 tance good exposures of rock and shale may be studied. North 

 of the quarry for thirty or forty feet extend thick, heavy beds of 

 encrinal limestone. They form a sharp contrast with the softer, thin- 

 ner layers in the quarry, — showing the change occurring in the same 

 rock within such short distance. Between this and the next ravine. 



