MIDDLE AND UPPER OEDOVICIAN. 219 



The two lower series — the Cat Head and the Lower Mottled — are not of any great thick- 

 ness, but are in the district readily distinguished from each other. The dividing line is placed 

 at a bed at which the mottled hmestone becomes highly charged with sihceous material in the 

 form of chert nodules, while the Hmestone above changes from a mottled grayish-white with 

 darker spots to a uniform buff, less crystalline rock. The faunal change is not very marked, 

 but it will be noticed that the numerous large cephalopods that characterize the lower are 

 almost altogether wanting in the middle division. 



The "Upper Mottled limestone" is described as varying in different localities 

 and in partial sections from hard mottled dolomite exhibiting rough surfaces marked 

 apparently by fucoids to soft, darker mottled impure earthy limestone which 

 passes into the overlying Stony Mountain formation. The thickness is estimated 

 at 130 feet near Winnipeg. 



The Stony Mountain formation is stated to represent the interval between the 

 top of the Trenton and the base of the Siliu"ian (upper). Dowling describes the 

 changes of thickness in strata which occupy this interval to the east and south 

 and says: 



Although this formation is supposed to thin out altogether in northern Minnesota, there 

 is found at Rosenfeld, in the southern part of Manitoba, a great thickness of shale beds between 

 hmestone formations which are probably Trenton and Silurian. At Stony Mountain the section, 

 although incomplete, in a known thickness below the Silurian of 110 feet, consists of shaly beds 

 in the lower part with thick-bedded hmestones above. The fossils from this part are mainly 

 from the shaly beds below the hmestone of the top of the section, and probably all these are 

 collected from less than 50 feet below the top of the formation. We might infer from this that 

 the upper part, that of which we have a section and a hst of fossils, is referable to the Rich- 

 mond group of Minnesota, and that the lower beds, mostly shales, are similar to the Utica of 

 the Cincinnati formation. One species only, characteristic of the Utica of Minnesota has been 

 found at Stony Mountain — PrimitieUa unicornis Ulrich. The majority of those common to 

 the two localities are from the upper parts of the sections. It is noted in the Minnesota reports 

 that several forms occurring in the Trenton appear in the Richmond group without any evi- 

 dence of their presence in the Utica. The same might possibly be asserted of some of the Mani- 

 toba forms, as several are found to range from the Trenton to the Stony Mountain formation. 



A complete list of fossils identified from these divisions of the Ordovician is 

 given in Bowling's report. The faunas were earlier discussed by Whiteaves.^^" 

 Ulrich in commenting on this correlation states : 



Dowling's determination of the Manitoba Ordovician formations is based entirely on the 

 Minnesota section of 1896. Much having been learned in the last 14 years concerning the 

 Ordovician of the middle and far West, it is desirable to revise the classification of the rocks 

 in both areas according to the present status of information. 



O 9. DBASE BIVEB, BRITISH COLUMBIA. 



Blackish graptolite-bearing slates occur on lower Dease River near its junction 

 with the Liard, in the belt of -unaltered Paleozoic rocks of the eastern Rocky 

 Mountains, near the sixtieth parallel. They were first seen in 1887 by G. M. 

 Dawson,^'*^ who states : 



From the second great bend to the mouth of the Dease the underlying rocks [underlying 

 supposed Triassic] consist of gray and black schists, the former generaUj'- calc schists and the 

 latter more or less highly carbonaceous. They are interbedded with thin limestones, which 

 often weather brown. The calc schists are frequently glossy and in some places form very 

 thin paper-hke layers. Some of these rocks closely resemble those met with at the "Grand 



