28 THE NAUTILUS. 



specimens are not fully matured. One of the two specimens has 

 been presented to the " Lea Collection," in the Academy of Natural 

 Sciences of Philadelphia. 



ON A COLLECTION OF MOLLUSKS FROM GRAND TOWER, ILLINOIS. 



BY FRANK C. BAKER. 



During the latter part of April and first part of May, Mr. Frank 

 M. Woodruff spent two weeks collecting birds in Jackson and Union 

 Counties, Illinois, and incidentally picked up a number of mollusks, 

 and the general conditions of the locality, and the small number of 

 shells collected seem to warrant a few notes. This locality is situa- 

 ted on the Mississippi River, north of Big Muddy River, in the 

 southwestern part of the State. 



Of the localites visited Mr. Woodruff says : " The shells were 

 found in a rocky glen or cleft in the center of the chain of high 

 precipices known by the names of Fountain Bluff, Devil's Bake 

 Oven and Backbone. This cleft or ravine begins about three-quar- 

 ters of a mile from the face of the cliff and gradually descends in a 

 northwesterly direction until the bottom is reached, and one may 

 stand upon a broad shelf of rock ten feet from the ground, with 

 high overhanging cliffs of bare rock on both sides. A stream of 

 clear spring water flows down this ravine and falling over the high 

 shelves of rock has formed numerous round pools or basins. I was 

 surprised to find no shells in the stream, and could only collect a few 

 specimens of Limncea humilis, which I found clinging to the wet 

 moss under the falls. The balance of the shells were found under 

 the moss and old logs at the base of the cliff. Fountain Bluff is five 

 miles from the town of Grand Tower, and is three miles long from 

 north to south and about one and a half miles wide. According to 

 Worthen's Geology of Illinois, the Backbone or ridge is formed by 

 an uplift of Devonian strata which is tilted to an angle of about 25, 

 and dips to the northeast. The bluffs consist of Chester limestone 

 and sandstone overlaid by conglomerate. The top of the bluff is 

 covered with a rich growth of timber, among which are Willow, 

 Sweet Gum, Qupelo tree, Sycamore, Cottonwood, Honey Locust, 

 Hock Berry, Box Alder, Red Birch, White Ash, Black Ash, Red 

 Oak, Mulberry, Persimmon, White and Black Oak, etc., are the 

 most common." 



