ART. 21 OBDOVICIAN TKILOBITES ULRICH 83 



seems to be nearly of the same age, but the Arenig, which succeeds it, 

 is more confidently assigned to the Upper Canadian. The Durness 

 on the northwest coast of Scotland belongs to another province and 

 is closely related to American formations of the Canadian. Its 

 lower part contains the Lecanospira fauna, which characterizes the 

 Middle Canadian in the Appalachian Valley, -Missouri, Oklahoma, 

 Texas, and many areas in western North America ; and its upper half 

 contains the similarly distributed Geratopea fauna which is equally 

 characteristic of the Upper Canadian. So far as known the Durness 

 comprises only Middle and Upper Canadian. In this respect it 

 agrees with the Canadian as developed in Missouri and northern 

 Arkansas and in Alabama, Tennessee, and most of the valley in Vir- 

 ginia. The lower Canadian series is differently and less widely dis- 

 tributed. In the Mohawk Valley in New York and probably also 

 in New Jersey no higher beds of the system are present. However, 

 in the vicinity of Ticonderoga, N. Y., again in central and southern 

 Pennsylvania, and thence southward through Maryland to some un- 

 known point in northern Virginia, and finally in the Arbuckle and 

 Wichita uplifts in Oklahoma the Middle and Upper Canadian lime- 

 stones are underlain by varying thicknesses of the lower series. The 

 observed maximum of 3,000 feet (Jonesboro limestone), is attained 

 at Limestone, Tenn. The section at this place is further unusual 

 because the excellently exposed Jonesboro limestone is directly suc- 

 ceeded by a 50-foot development of Lenoir limestone and this by 

 Athens Shale. 



A small variety of Dldymograptus hifidus is said to occur in the 

 basal part of the Llandeilo. In America we have two small varieties 

 of this graptolite, and both occur near the boundary between the 

 Canadian and the Ordovician. One occurs in Lawrence County, 

 Arkansas, near the top of the Black Rock limestone, which is the 

 youngest of the Canadian formations in the Mississippi Valley. The 

 other occurs near the base of the Joins limestone with which the 

 Ordovician (Ulrich), begins in Oklahoma. Which of the two is 

 most like the Llandeilo variety remains to be determined. 



SUPPLEMENTARY NOTES ON THE GIRVAN DISTRICT SECTION 



In deference to my belief that the Ordovician formations of the 

 Girvan District named in the middle part of this column are with 

 two exceptions not strictly correlatable with Appalachian formations, 

 I have placed the names of most of them in midway positions with 

 respect to those of the latter. The following notes on the Girvan 

 section, which became possible only since my visit to Girvan the 

 past summer with Prof. O. T. Jones and other British and American 

 members of the Princeton University Summer School of Geology in 



