8 OLAF HOLTEDAHL. [SEC. ARC. EXP. FRAM 



is very finely granulated all over, the other not so on the glabella. 

 Together with these specimens we find the remains of a trilobite of 

 quite another type. We have two fragmentary central portions of the 

 cephalon, which undoubtedly belong to an Illcemirus sp. (see pi. 4, fig. 4) 

 hut it is not possible to make any exact determination. The lllcenurus 

 forms is typical of the lowest ordovician in N. America. Only one 

 form, /. quadratus HALL, is given from the Potsdam Group. 



Other forms belonging to this younger type of fauna include one 

 small fragment of a head of a Lichas sp. 



SCHEI further describes the beds thus : - 



"On the top of this light-coloured limestone with its fossil ortho- 

 cerites lie less strongly developed strata of quartz sandstone, alternated 

 with limestones, and on the top of that again a bed of close-grained 

 brown limestone, about 100 feet thick, some of the layers of which are 

 fossiliferous. 



The fossils in this case are just as fragmentary as in the under- 

 lying limestone. Most commonly we find gastropodes, preserved as 

 casts. 



In some pieces we see very frequently a little slender form with 

 numerous coils (see pi. 4, fig. 6) which cannot easily be separated from 

 varieties of the common Hormotoma gracilis HALL, which has a very 

 wide vertical extension within the Ordovician. Another form, which 

 the specimens before us greatly resemble, is that described by HALL and 

 WHITFIELD from the Pogonip Group in Nevada. Fusispira compacta. 

 As regards other gastropodes we find one incomplete specimen of a 

 Madurea sp. (see pi. 4, fig. 8). Some fragments of trilobites also 

 occur. Great interest will be attached to a quite small, badly preserved 

 pygidium with hollowed outer rim (pi. 4, fig. 7). It has a Cambrian character 

 and presumably belongs to a Bathyuriscus or Ptychoparia form. 

 Although these few fossil remains do not give any particularly good 

 data for the age of this horizon, yet it suggests that the limestone 

 in reality is only slightly younger than the underlying limestone rich 

 in orthocerites. Both zones are presumably to be classified in the lowest 

 Ordovician transition horizon. 



A section of a limestone conglomerate taken from a piece collected 

 above the limestone with orthocerites at Victoria Head is shown in 

 pi. IV, fig. 11. 



