APPLICATION OF PRINCIPLE OF TRANSGRESSIVE OVERLAP 591 



strata. Higher up in the series occurs Pseudomonotis pealei, represent- 

 ing the lower Jakutic stage. Less than 30 miles east, in the Salt Kiver 

 range of Idaho, the Pseudomonotis pealei beds rest on limestone with 

 Productus multistriatus* thus indicating an eastward overlap. 



In the Humboldt mountains of Nevada the Star Peak group of more or 

 less arenaceous limestones, which represents the middle and upper Mus- 

 chelkalk horizon (Anisic and later), rests on the metamorphic Koipato 

 formation. If no lower horizon is observed in the Star Peak series, an 

 eastward overlap is indicated, since the Meekoceras beds are present in the 

 Inyo mountains of eastern California. 



A typical case of overlapping of formations due to the encroachment of 

 the sea exists in the Shasta-Chico series of Oregon, Washington, and 

 British Columbia. The series rests unconformably upon an old land sur- 

 face composed of more or less metamorphosed strata, ranging in age from 

 Paleozoic to Jurassic and complicated by igneous intrusions. A basal 

 sand or conglomerate is generally present and sometimes seems to grade 

 downward into the rocks of the old land, owing to the apparent slight 

 rearrangement of the disintegration soil formed by the decay of the 

 crystallines. The Lower Shasta or Knoxville beds extend north to the 

 Shasta county line in California, where they are overlapped by the Upper 

 Shasta or Horsetown beds, which extend 125 miles beyond the Knoxville. 

 In this distance the higher beds of the Horsetown progressively overlap 

 the lower ones. Where the Horsetown beds come to an end, the Chico 

 overlap them, resting unconformably on the metamorphics. "The sub- 

 sidence continued until the sea reached the western base of the Sierra 

 Nevada, near the fortieth parallel, and all or nearly all that part of 

 California north, northwest, and west of Lassen peak, as well as almost 

 the whole of Oregon, was beneath its waters." f 



Foreign examples. — The Hils of Germany has long been recognized as 

 a typical basal formation of the transgressing sea of early Neocomian 

 time. This formation consists of a series of clays, with sandstones and 

 conglomerates at the base. They rest, with an hiatus, on various members 

 of the upper Jura from Kimmeridgian to Purbeckian, containing peb- 

 bles and worn fossils of these in the basal bed. The age of the basal bed 

 of the Hils varies, ranging from lowest Neocomian to post-Wealden, as 

 shown by the succeeding fossiliferous clays in the various localities. This 

 rise of the basal bed in the column marks the progressive advance of the 

 Neocomian sea over central Europe. 



A comparison of the English and Irish Cretacic brings out an interest- 



* A. C. Peale : Bull. U. S. Geological and Geographical Survey, vol. v, no. 1, p. 121. 

 t J. S. Diller : Bull. Geol. Soc. Am., vol. 4, p. 27. 



