JUEASSIC. 577 



B 3. NORTHWESTERN ALASKA. 



The coast northeast of. Cape Lisburne exhibits a section of strata constituting 

 two formations, the lower one coal bearing and according to its fossil plants of 

 Jurassic age, the upper one unfossiliferous. Collier ^^^^■'^^^^ has described these forma- 

 tions as follows : 



Mesozoic rocks occur on the coast about 3 miles east of Cape Lisburne and extend beyond 

 the limits of the area covered by this investigation. They consist of two members, of which 

 the older is coal bearing while the younger is not only destitute of coal but also of fossils. 



The coal-bearing member, which has been called the Corwin formation, begins on the coast 

 line about 26 miles east of Cape Lisburne and about 2 miles west of Corwin Bluff. ' From this 

 point it extends eastward to and beyond Cape Beaufort, the eastern limit of the area comprised 

 in this investigation. This formation consists of rather thin bedded shales, sandstones, and 

 conglomerates. The shales which form the greater part of the section, vary from greenish-brown 

 calcareous to black carbonaceous beds, and in texture from mudstones to fine-grained sandy 

 shales. 



The sandstones occur at infrequent intervals through the formation, in beds usually less 

 than 10 feet in thickness. Their outcrops form low ridges, which are easily traceable over 

 eroded areas. The conglomerates are made up mainly of quartz and chert pebbles, ranging in 

 diameter from one-half to 4 inches. A conglomerate bed about 15 feet thick, which reaches 

 the coast at Corwin Bluff, makes a distinct ridge from 100 to 200 feet high, which has been 

 traced southeastward for about 15 miles, giving a definite key to the stratigraphy of a portion 

 of the field. 



The thickness of the Corwin formation exposed along the coast near Corwin Bluff is not less 

 than 15,000 feet. The base of the formation has not been observed, but it probably rests uncon- 

 formably on the Paleozoic rocks. 



Fossil plants collected from it indicate that the age is Jurassic. . 



The structure consists of several broad synclines and anticlines, the dips of the beds varying 

 from 0° to 60°. There is no evidence of faulting other than minor shearing movements parallel 

 with the bedding planes. 



The Corwin formation is conformably overlain by a more arenaceous series of sandstones 

 and shales in which neither coal beds nor fossils have been found. The contact of these rocks 

 with the Corwin rocks may be seen about 2 miles west of Corwin Bluff, whence it extends south- 

 eastward for several miles to the limit of the area investigated. The western limit of the forma- 

 tion is a well-defined fault line extending southeastward from a point on the coast 3 miles east of 

 Cape Lisburne, where the formation is in contact with the Paleozoic, which is overthrust. The 

 structure of this formation increases in complexity from its base at the top of the Corwin forma- 

 tion as this fault is approached; there are intense crumpling and numerous minor thrust faults. 

 For this reason it is impossible to estimate the thickness of the formation, but the evidence 

 obtained indicates that its minimum thickness is not less than 5,000 feet. 



R-S 27. NORTHEAST COAST OF GREENLAND. 



Nathorst ""^^ gives the following description of the Jurassic strata on the north- 

 east coast of Greenland : 



Jurassic strata occur at two localities on Kuhn Island, on the south side and on the east 

 side. At the first-mentioned place they consist of brownish fine-grained sandstones, with an 

 inclusion of coal strata. There are in the sandstones fossils which, according to Youla, indicate 

 the Middle Dogger. Of quite a different age are the sandstone and marl beds that are found 

 about the easternmost point of the island ; they are distinguished by a great richness in forms 

 from the family AuceUa, and further of PerispMnctes payeri, Belemnites panderianus, besides 

 others, and are therefore referable to the youngest Jurassic, the Aucella beds. The Jurassic at 

 both localities is given as resting directly on the Archean. * * * 

 48011°— 12 37 



