22,2 The American Geologist. ^p"^- i^^^- 
of geologic time. At about the opening of the Quaternary 
era, the territory was warped into a series of broad, compar- 
atively low arches and domes. *Earlier, but yet at a time post- 
Cretaceous in age, the same region had been acted on by oro- 
genic activity, the result being a series of structurally enclosed 
basins, separated by broad ridges which were high in compar- 
ison with those formed at the opening of the Quaternary era.f 
The products of these two periods of orogenic activity were 
characteristically different from that of an earlier period which 
appears to have affected the region at about the close of Jur- 
assic time. The Early Tertiary and Early Quaternary deform- 
ations were like those which have been shown to have operated 
on the Southern Appalachian province in post-Cretaceous times,"! 
while the first post-Jurassic disturbance of the Klamath region 
was essentially of what is known as the Appalachian type, be- 
ing characterized by great folds and faults, with axes extend- 
ing for hundreds of miles in a certain direction common to the 
system. The broader structural features of the Klamath re- 
gion are principally due to this post- Jurassic disturbance and 
my remarks in the succeeding pages will treat of it chiefly. 
The pre-Cretaceous stratified formations involved in the 
Klamath mountains west of the Sacramento river consist of, 
three series, a highly metamorphic series of schists, supposed 
to be of pre-Cambrian age, probably Algonkian, possibly 
Archaean ; a series of less highly metamorphosed slates, quartz- 
ites, limestones and cherts, of an age ranging from early in the 
Devonian to the close of the Carboniferous period ; and a Mes- 
ozoic series also altered by metamorphic action, but less in- 
tensely than the Paleozoic series. § The first series consists 
chiefly of the Abrams mica schist, which is supposed to have 
an exposed thickness of about looo feet ; and overlying it, the 
Salmon hornblende schist, known to be at least 2500 feet thick. 
Probably the real thickness of these formations is much 
greater. 
* "Neocene Deposits of the Klamath Region, California," Journal of 
Geology, vol. x, No. 4, Maj^-Jnne, 1902. 
t "The Significance of Certain Cretaceous Outliers in the Klamath Region, 
California," Am. Jour. ofSci., vol. xiv, July, 1902. 
J "Geomorphology of the Southern Appalachians," National Geographic 
Magazine, vol. vi, pp. 63-126. 
§ "Metamorphic Formations of Northwestern California," American 
Geologist, vol. xxvii, April, 1901. 
