324 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Raymond's notes on the Threeforks shale refer to the type locality in south- 

 western Montana. He says in part: ^^^ 



It is the purpose of the present paper to announce the discovery in the Threeforks shales, 

 near Threeforks, Madison County, Mont., of an Upper Deronian fauna containing Clymenia, 

 Entomis, and goniatites. 



* * * * ***** 



The Threeforks shales were divided by Dr. Peale into three portions: 



Feet.' 



3. Upper shales, with many fossils .' 65 



2. Grayish-brown limestone, without fossils 15-20 



1. Lower shales, without fossils 50 



Division 3 is subdivided as follows : 



Feet. 



D. Yellow sandstone, the lower part calcareous 25 



0. Coal-black shale 5 



B. Gray limestone 10 



A. Green shales with bands of limestone 30 



* * * * ***** 



In the 65 feet of strata constituting the upper shales at Threeforks there are five zones in 

 which the hthology and faunules diflfer somewhat. 1, 2, and 3 make up A above; 4 is the same 

 as B; and 5 equals D. From C no fossils were obtained. These zones, beginning with the 

 lowest, are as follows : 



1. Red shale zone. — The shales of this zone are hard, reddish, and fissUe, the layers weather- 

 ing into small, sharp-poiated fragments. The fossils are preserved in pyrite, which is often 

 partially altered to limonite, and they weather out on the surface in numerous bare spots along 

 the strike of the beds. * * * 



2. Green shale zone. — These are the green shales described by Peale (part of A, above). 

 Fossils abound and further collecting should reveal a much larger fauna. Clymenia and Entomis 

 are abundant, associated with a great number of brachiopods and lameUibranchs. * * * 



3. White hlocky shale. — The exact horizon of this zone is not known, as the fossils were 

 obtained at a locahty where the layers seemed to be somewhat disturbed. In the field it 

 appeared to be above the green shale, but it could not be located in any place where the beds 

 were undisturbed. The faunal list is short, but the fossils are abundant. * * * 



4. Gray limestone zone. — This limestone weathers readily and produces great quantities 

 of fine fossils, mostly brachiopods. Two species of Clymenia occur in this zone, but the gonia- 

 tites are very rare. This same Hmestone is well exposed in the Devonian ravine at Logan, but 

 no specimens of Clymenia were found at that locahty; it has, however, furnished two fragments 

 of cups of crinoids, one of which has been identified as a species of Mariacrinus, by Mr. Frank 

 Springer. This is of interest, as it is the first crinoid reported from the Devonian of the Rocky 

 Mountains. * * * This seems to be the upper limit of the range of Clymenia. 



5. Yellow sandstone zone. — This sandstone or sandy limestone forms the capping bed of 

 the Devonian both at Threeforks and at Logan. A few beds are very fossiliferous and the 

 fauna indicates a transition into the Mississippian (Madison limestone). "^ 



L 18. ST. HELENS ISLAND, MONTREAL. 



A very small exposure of Devonian agglomerate on St. Helens Island, Montreal, 

 has yielded Devonian f ossUs that appear to present a unique association. Schuchert^'^ 

 reviewed the faunas and the conditions of their occurrence and concluded: 



The foregoing evidence shows clearly that two distinct faunas are represented on St. Helens 

 Island — one, the Helderbergian, older than the agglomerate, and another, from a block m the 

 agglomerate, of Middle Devonic age. 



"For lists of fossils from the several zones see the work cited. — B. W. 



