312 The American Naturalist. [April, 
laid by a stratum of soft, coarse sandstone. In this connection it 
might be objected that the above explanation would make the de- 
posit of sandstone contemporaneous with the growth of some 
portions of the coral reef, in which case it should contain some 
internal proof of proximal relations. Such proof is not wanting. 
On the Iowa side of the Mississippi river, one-half mile above 
Keokuk, the brecciated limestone is overlaid by fifteen feet of 
this sandstone, which is somewhat harder than usual elsewhere, 
forming a projecting ledge. At this locality the writer has ob- 
served a mass of Lithostrotion canadense five or six inches in 
diameter imbedded in the lower portions of the sandstone, about 
two feet above the base.. The presence of the coral here is ac- 
counted for on the supposition that at some not distant point a 
coral reef was growing at the time this sandstone was deposited. 
By the action of the waves this mass was broken from its bed and 
driven along the shallow bottom to find at last a resting-place in 
the mud and detritus brought in from the neighboring land. That 
the distance may not have been great may be inferred from the 
known fact that in coral regions the transition from a bottom of 
coral detritus to one of mud or earth is often very abrupt.” 
From the above we submit the following brief 
RECAPITULATION : 
1. The Upper Division of the St. Louis Beds is a limestone 
‘ which in its northern extension is decidedly brecciated and 
irregular in stratification and thickness. In the interior, with a 
‘few exceptions apparently due to littoral conditions, the rock is 
of a fine-grained, even texture, and regular stratification. 
2. No adequate cause for this prominent feature of the lime- 
stone has thus far been advanced. While present in the attenu- 
ated margins of some limestones, it is not in all, and hence would 
imply the existence of other ‘than littoral conditions alone. 
3- Another significant feature accompanying the brecciated 
structure of this limestone is its odlitic character. 
1 Dana, Manual, p. 623. _ 
