LOCAL GEOLOGY OF DAVENPORT BARKIS. 261 



Watson. The followiug description is from Proc. Amer. Acad., XII, 



1877 :— 



Amarantus (Ptxidium) blitoides, Watson. — Prostrate or decumbent, the 

 slender stems btcomino; a foot or two long, glabrous or nearly so; leaves 

 broadlj^ spalulate to narrowly oblanceolate, attenuate to a slender petiole, an 

 inch long or usually less; tlowers in small contracted axillary spikelets; 

 bracts nearly a line broad. — Frequent in the valleys and plains of the interior, 

 from Mexico to N. Nevada and Iowa, and becoming introduced in some of the 

 Northern Slates eastward. It somewhat resembles the A. Biitum, L., of the 

 Old World, and has been mistaken for it. 



Aster Novi-Belgii (No. 371) is to be omitted from the list. The speci- 

 mens on which the determination was made, prove to belong to a much 

 commoner species. 



A few very interesting names are withheld for further verification. 

 Collectors will confer a favor if they will forward information in regard 

 to the State flora. It is proposed to publish additions as fast as consis- 

 tent with accuracy. 



Botanical Laboratory., Agricultural College, Ames, loiva; August, 1874. 



The Local Geology of Davenport and. Vicinity. 



BY REV. W. n. BARRIS. 



Read Oct. :6th, 1877. 



We are indebted to Prof. Hall for the first detailed description of the 

 rocks in our vicinity. In his report on the Geological Survey of the 

 State of Iowa he has described them under two natural divisions— ^^rsf, 

 limestones of the Upper Helderberg, and second, limestones and shales 

 of the Hamilton Group. 



The first embraces the series of limestones that stretch away a mile or 

 two aboj^e the city, seen in ledges immediately fronting the river, and 

 found also in heavier beds lying back in the blufEs. On Duck Creek is 

 an exposure, attaining a thickness of from thirty to forty feet. Denuded 

 of its uppermost layers, this rock forms the substratum on which Eock 

 Island rests, and into which are sunk the foundations of the various 

 Government buildings now in process of erection. Below Davenport a 

 mile or more it crops out on the river bank, or lies just below the surface 

 soil of the river bottoms. It has furnished abundance of the most dura- 

 ble and massive building material. The latest built stone churches in 

 the city have been constructed of this rock — the Cathedral from the non- 

 fossiliferous quarries above the city, Trinity Church from the fossiliferous 

 quarries below. The character of the bedding is exceedingly variable. 

 There are heavy courses of over a foot in thickness, giving every evi- 

 dence of toughness and durability. There are layers, splitting into 

 laminiE of an inch and less in thickness, the very type of brittleness and 

 decay. A fine grained compact limestone, often alternates with a sub- 

 crystalline form. Strata are distinguished by an extended continuity 

 of surface, or interrupted by irregular masses of clay. And yet what- 



[Proc. D. A. N. S. Vol. II.] 35 [Sept. 1878.] 



