The Jurassic Horizon. — Keyes. 289 
Glacial period, by its testimony of very great preglacial land 
elevation, together with the similar evidence given by the 
submarine continuations of the Congo, the Adour, and other 
rivers, and by the profound depths of the Scandinavian and 
Arctic fjords. 
THE JURASSIC HORIZON AROUND THE SOUTHERN END OF 
THE ROCKY MOUNTAINS. 
By Charles R. Ketes, Socorro, New Mexico 
Soon after passing the Colorado line the Rocky moun- 
tains rapidly lose their predominant characteristics and 
fade out completely into the Mexican tableland. The moun- 
tain ranges which succeed to the southward are short, iso- 
lated, tilted blocks, that are of a wholly different type from 
that of the mountainous structures to the northward, and 
to which they present marked topographic contrasts. 
At this southern extremity of the Rockies in northern 
New Mexico, the general stratigraphy presents some un- 
looked for phases that are of exceptional interest. More- 
over, it is here that the eastern Mississippi valley strati- 
graphy, with which American workers are most familiar, 
loses its identity and is replaced by a less known western 
stratigraphy. The rock-successions of these two provinces 
have never been satisfactorily or exactly paralleled. Of the 
many stratigraphic problems that have arisen recently for 
solution in this region none has possessed greater interest 
than the questions surrounding the horizon at which the 
Jurassic system should be represented. 
Ever since the time of Jules Marcbtfs trip, sixty years 
ago, in connection with the Pacific railroad expedition along 
the thirty-fifth parallel, when he pronounced the now cele- 
brated Tucumcari section in eastern New Mexico as of 
Triassic and Jurassic ages, there has been waged one of the 
bitterest and most useless controversies in the history of 
American geology. Marcou was well acquainted with Ju- 
rassic and Triassic sections of Europe and, as Louis Agassiz 
has well remarked,* he could hardly be blamed for seeing 
* Am. Jour. Sci., (1), vol. xxvii, p. 134, 1859. 
