IOWA ACADEMY OP SCIENCES. 
55 
The degree of induration, the pronounced jointing, and the 
general ancient aspect of this conglomerate render it rea- 
sonably certain that it is not a part of the drift which overl es 
it. But it has pebbles of Archaean rock, and one of these was 
nearly six inches in diameter. None of them were observed to 
be scored, though quite a number were examined. The aver- 
age size of the pebbles is from one-fourth to two inches in 
diameter. On the other hand, it is not believed that it can 
belong to the coal measures. Some of the pebbles appear to 
be pieces of coal measure concretions and lumps of coal meas- 
ure clay, and the aggregation of rocks represented in the 
pebbles is unlike anything observed in the coal measure con- 
glomerate. For comparison, a collection of fifty pebbles was 
made, representing the average sizes. The proportion of 
specimens of different rp)cks in this lot was as follows: 
Yellow chert A 32 per cent 
Greenstone 26 “ “ 
Granite (mostly red) 10 “ “ 
White quartz (some of a faint, pink color) 8 “ “ 
Fragments of coal measure rock 4 “ “ 
Light red orthoclase 2 “ “ 
Black felsite *. 2 “ “ 
Porous Niagara chert 2 “ “ 
Chalcedony 2 “ “ 
Orthoclase-biotite rock 2 “ ‘‘ 
The only conclusion which can at present be drawn, as to 
the age of this conglomerate, is that it is post- Carboniferous 
and preglacial. Dr. Calvin, who has seen it recently, pro- 
nounces it identical in nature to the Rockville conglomerate 
described by McGee. It also somewhat resembles the Cretaceous 
conglomerate found in Guthrie county by Mr. Bain. Possibly 
it may be an outlier of the Lafayette formation, observed far- 
ther south by McGee and by Salisbury. 
In the south bluff of West Hill in Muscatine, just east of 
Broadway street, there lies on top of the coal measures and 
under the drift a small remnant of a conglomerate somewhat 
resembling that above described. It is seen for a distance of 
only three or four rods and its greatest thickness is three feet. 
It is plainly unconformable with the beds below. The base is 
a very pebbly sand, held in a dark ferruginous matrix, which, 
in some places, does not wholly fill the interstices between the 
pebbles. The upper surface is a brown ferruginous, moder- 
ately fine sandstone of about the same hardness and aspect as 
