l-i'2 L'hi Ann fKil II (ii oint/isf. Septenibtr, 18'J1 
ADDITIONAL NOTES ON THE DEVONIAN ROCKS 
OF BUCHANAN COUNTY, IOWA. 
By S. Cai.vin, Iowa City. 
The present paper is intended as a preliniinarv notice of some 
observations reeentlj' made on the Devonian rocks of Buchanan 
county. Iowa. In the final paper on the sul)ject references to the 
literature on the Devonian of this part of Iowa, and due credit 
to those who liave previously worked in this field, will be given. 
In a paper published in the Bulletin of the United States Gfo- 
logicdl mid freoi^riip/ti(<il Sitrceij i}f the Tirritoriis. Vol. IV. 
Xumbcr 3, Jtdi/ 29, 1878, pp. 725-7:5(». I referred, under the 
name of The Lidipendmee shnlra, to a meml)er of the Devonian 
series that at that time was supposed to lie at the Viase of the 
system in Buchanan county. Later oljservations render it cer- 
tain that the Independence shales do not constitute the lowest 
member of the series, but that they were preceded by brecciated 
limestone of Devonian age. The thickness of this brecciated 
limestone, so far as it is developed in Buchanan county, has not 
been ascertained. It is. however, well expensed in the bed of the 
Wapsipinnicou river at Independence. At Troy Mills, in Linn 
county, about a mile from the southern boundary of Buchanan, 
it is again exposed. It may l)e seen at a number of intermediate 
points. A ver^' perfect limestone breccia, having an estimated 
thickness of about thirty feet, and l)elonging proV)ably to the 
same horizon as the lirecciated limestones of Buchanan county, 
is exposed in a deep railway cut at Fayette. I<jwa. 
So far then as Buchanan county is concerned the exposed strata 
are : 
i. Brerriated Uiiuxtonv. No fossils have as yet been seen in these beds 
at Independence, but at Troy Mills in Linn county, they contain many 
brachiopods that are characteristic of the lower part of the Iowa 
Devonian. 
2. The, Imhpendeiiei' .^hideif, composed largely of bluish shales with 
some layers that are black and highly carbonaceous, and containing occa- 
sional pyritized plant stems and fragments of coal. The peculiar fauna 
of these shales and its interesting relation to the fauna of the Rockford 
shales along Lime creek in Floj-d and Cerro Gordo counties has been 
discussed in the article above cited. 
.}'. (inniri-niK hcdx. These are beds of rather hard, compact limestone a 
few feet in thickness and containing numerous specimens of a large 
Gi/rortriix with which are associated robust forms of (iyiudnhi oiridin- 
t'iU.f Hall, or PeutumertiK comi>f Owen, of Walcottand some otlier authors. 
