522 E. M. Kindle — Section at Cape Thompson, Alaska. 



westerly outcrops near Cape Thompson, whence it trends 

 northerly or northwesterly. Near the middle of this syncline 

 along the coast, the rocks lie nearly or quite horizontal for 

 more than a quarter of a mile. From the horizontal they pass 

 gradually into the inclined position, showing dips on opposite 

 sides of the syncline toward its axis. These increase from five 

 or ten degrees nearest the center to a maximum of about 40° 

 on the southeast and 90° on the northwest. This synclinal 

 structure is expressed in the areal distribution of the rocks by 

 two parallel belts of Carboniferous limestone separated by a 

 band of Mesozoic shales one and a half or two miles in width. 

 Toward the south side of the syncline the transition from very 

 slight to steep dips is gradual and progressively uniform from 

 the nearly horizontal Mesozoic shales to the highly inclined 

 limestones, where the dip is uniformly about 35 degrees. 



On the west side, however, the uniformity of the syncline 

 is broken up by a local anticline about 300 feet in width, 

 known as agate rock. This minor structural modification of 

 the syncline shows most intricately crumpled and broken beds 

 below the belt of regularly arched strata at the top, which give 

 it the appearance of a typical anticline when seen from a little 

 distance. This local fold is shown in a photograph published 

 by Collier.^ The Carboniferous limestones comprising Cape 

 Thompson on the northwest side of the syncline also show 

 marked irregularities in dip. That these irregularities are not 

 evident from a distance is indicated by Collier'sf sketch of the 

 section, which was made from the deck of a steamer at a dis- 

 tance of about 3 miles from the Cape. It indicates a uniform 

 westerly dip for the limestones. Nearly the same inclination 

 is indicated for them in the section by Lieut. Belcher J of Capt. 

 Beechey's expedition. Instead of a uniform westerly dip, the 

 beds at the Cape are generally inclined toward the east at vari- 

 ous angles ranging from 90° to horizontal. The most westerly 

 beds exposed at the Cape include about 400 feet of shales and 

 sandstones which dip toward the east or the axis of the syncline 

 already described at from 80° to 90°. The Carboniferous 

 limestone lying between these basal shales and the Mesozoic 

 beds are generally inclined where observed toward the east at 

 angles ranging from 25° to 90°. 



Age of the Formations. 



The lowest beds exposed at Cape Thompson outcrop along 

 the beach immediately north of the cliffs. The rocks exposed 



* Collier, A. J., Geology and Coal Resources of the Cape Lisburne Eegion, 

 Alaska, Bull. U. S. Geol. Survey No. 278, pi. 4, fig. A. 



fBull. U. S. Geol. Survey No. 278, p. 21, 1906. 



% Buckland, W. , Geologv and Zoology of Capt. Beechey's Voyage, London, 

 Henry V. Bohn, 1839, pp." 171-174. 



