TERTIARY 337 



The fossils which were secured from the ferruginous concretions occur- 

 ring in division 5 of the section were referred to Dr W. H. Dall, who 

 reports that "one resembles TJnio onariotes Mayer from the Kenai forma- 

 tion, another Anadonta atlilios Ma3^er of the same beds, but they are 

 probably not identical. The beds are probably Oligocene or Upper 

 Eocene, like those of Kenai/' 



Considerable interest attaclies to these fossils in connection with their 

 bearing on the distribution in Tertiary times of the Naiades, a group of 

 fresh-water lamellibranchs represented in the present streams and lakes 

 of lower latitudes in North America by several hundred species. 



Maddren and McConnell have reported two basins similar to the 

 Coleen, but larger, higher tip the Porcupine a short distance east of the 

 International boundary. One of these has an approximate length of 100 

 miles and a width of 60 miles. No fossils were obtained by McConnell 

 from these upper basins, but the description which he gives of the beds 

 exposed corresponds so closely to the sections observed by the writer that 

 it is highly probable that the age of the beds in the basins on the two 

 sides of the boundary is the same. McConnelP^ expressed a similar opin- 

 ion concerning the equivalence of the beds in question, but presented no 

 paleontologic evidence of the age of the beds in either of the basins which 

 he described. 



LAVAS 



In the Upper Eamparts the Porcupine has cut its gorge for a consider- 

 able distance through an extensive sheet of lava. This lava sheet extends 

 from a point 10 miles below the International boundary nearly to the 

 lower end of the Upper Ramparts as a continuous sheet, except for a 

 break of about a mile below Salmontrout river. The lava beds rest on a 

 highly irregular surface of Paleozoic rocks. The latter in many places 

 form the lower portion of the gorge walls, while the lavas form the upper. 

 Between the Eapid and Salmontrout rivers the walls of the gorge are in 

 places composed entirely of lava. ' In this part of the river the lavas have 

 a thickness of not less than 300 feet. The lava sheet is made up of sev- 

 eral successive flows. At one point evidence of four successive flows was 

 observed. Several of the successive flows were separated by intervals 

 sufficiently long for the accumulation of soil and forest growth. This is 

 shown by the following section, taken near the eastern margin of the 

 sheet : 



" R. G. McConnell : Report on an exploration in the Yulvon and Mackenzie bastna, 

 Northwest Territory. Canadian Geological Survey, vol. 4, new series, Report D, 1890, 

 pp. 128, 132. 



