Persona/ and Scientific Wews. -545 
are called diorite-gneisses because the feldspars are chiefly of the oligo- 
clase-andesine series. 
Mr. Whitman Cross read a paper on 
The Diorite of Ophir Loop and its Inclusions, with suggestion as to 
the origin of certain gneisses. The diorite at this locality is a lateral 
arm of a stock which cuts up through Cretaceous sedimentary rocks 
and a bedded volcanic series of Tertiary andesites. The lateral offshoot 
from this stock is intruded as an irregular sheet between the Dakota 
Cretaceous and the upper Jurassic, reaching a thickness of 1,000 feet. 
In its lower portion it is locally very full of included rock fragments. 
These inclusions were described, and specimens were exhibited. They 
are interpreted as genetically connected with each other and with the 
diorite magma, which brought them to their present position. 
The diorite is a variable rock, with augite and hornblende. The in- 
clusions vary from feldspathic rocks, poor in dark silicates, to black 
amphibolites nearly free from feldspar. They are developed in granular 
and banded forms, and exhibit all manner of gradations in structure as 
well as in composition. 
The study of these rocks led to the stated conclusions that quite local 
differentiation has gone on in the depths from which both diorite magma 
and inclusions came, and further, that a shearing movement of the dif- 
ferentiated magma, followed by consolidation, produced rocks greatly 
resembling many gneisses, amphibolites and schists, and especially those 
of the Archean complex. It was suggested that some gneisses and 
associated rocks of unexplained or assumed metamorphic origin may be 
primarily banded igneous rocks, which should be considered with their 
massive equivalents rather than with secondary schists of similar con 
stitution. 
The meeting of this society of April 8th was devoted to a 
general discussion of the subject of the application of strati- 
graphy and paleontology in determining subdivisions of 
geologic time. 
The broad problems involved in the announced topic were primarily 
presented by Mb. Whitman Cross in a concrete case. He described 
the present state of knowlege regarding the formations of the Rocky 
Mountain region belonging to the periods between the marine Cretaceous 
and the Wasatch Eocene, including the Laramie, Arapahoe, Denver, 
Ft. Union, and Puerco. The stratigraphic relations as at present known 
were described and then the facts of the fossil floras, the invertebrate 
and the vertebrate faunas were summarized. From the facts given it 
appears that the geologist investigating the formations of the group 
named is confronted by much conflict of evidence as to the relative im- 
portance of the time intervals separating the epochs of sedimentation. 
This is especially true in respect to the drawing of aline between the 
Meso/.oic and (Vnozoic in this region. The conflict of evidence in this 
instance was cited to show the necessity for a careful examination as to 
the nature of the connection between great fauna] changes and the con 
temporaneous events of stratigraphic history. It appears that all forms 
of life were able to survive withoul radical change the period of greal 
orographic disturbance al the close of the Laramie proper, and thai the 
dominant vertebrate life of the post- Laramie disappeared at the close of 
that epoch from causes as yet unknown, which did not effect in any 
corresponding degree the contemporaneous plant and invertebrate life. 
Mr. K. H. Know lion presented a review of the fossil floras of the 
Laramie. Arapahoe, Denver, and Ft. Union formations, showing the 
strong distinctive characters of each and also their intimate relation 
ship. This evidence fails to indicate any one break of supreme impor 
tance in this series of epochs. 
