424 Scientific Intelligence. 
igneous masses into the sedimentary complex; on the other - 
hand, the rock type produced by the consolidation of these mag- 
mas has been found to have characteristics worthy of special note 
in the bearing upon the principles of petrography.” The author 
has had not ‘only his own investigation in the Colorado region, 
but the admirable work of Gilbert, Peale, Holmes, and others to 
furnish him with the facts necessary to a comprehensive discus- 
sion of the phenomena concerned. 
Mr. Keith’s paper is an exhaustive discussion of a typical piece 
‘of geological structure in the midst of the Appalachian region. 
“'The Catoctin belt,” the author states, “has shown itself to be an 
epitome of the leading events of geological history in the Appa- 
lachian region. It contains the earliest formations whose original 
character can be certified; it contains almost the latest known 
formations; and the record is unusually full, with the exception 
of the later Paleozoic rocks. Its structures embrace nearly every 
known type of deformation. It furnishes examples of every 
process of erosion, of topography derived from rocks of nearly 
every variety of composition, and of topography derived from all 
types of structure except the flat plateau type. In the recurrence 
of its main geographic features from pre-Cambrian time till the 
present day it furnishes a remarkable and unique example of the 
permanence of Continental form.” In the paper the leading 
geological events which have left their impress on the region are 
traced and their effects recorded. 
Mr. Diller’s paper is another comprehensive study of the geo- 
logical history of a region, that of Northern California, the 
borders of the Sacramento Valley, in the Klamath Mountains 
and the western slope of the Sierra Nevada. The author finds 
this region practically reduced to a baselevel condition during 
the early portion of the auriferous gravel period. ‘ The mountain 
ranges were low, and the scenery was everywhere characterized 
by gentle flowing slopes... . The topographic revolution con- 
sisted in the development out of such conditions of the conspicu- 
ous mountain ranges of to-day. The northern end of the Sierra 
Nevada has since been raised at least 4,000 feet, and possibly as 
much as 7,000 feet, and a fault of over 3,000 feet developed along 
the eastern face of that portion of the range. The Klamath 
Mountains may in some portions have experienced at the same 
time an equal upheaval. From both sides the amount of uplift 
decreases rapidly toward the Sacramento Valley. In the initial 
part of this revolution the earlier auriferous gravels were found. 
The source of their material, of which, next to gold, quartz is the 
most important, was found in the thick deposit of residuary detri- 
tus which had accumulated upon the surface of the land during 
the baselevel period. The large mass of disintegrated rock sub- 
stance rendered the loading of the streams so easy that when 
rejuvenated by orogenic movements they readily became over- 
loaded and filled their ancient channels with auriferous gravels.” 
The two papers, by Messrs. Lindgren on the gold-silver veins of 
