90 
IDDINGS. 
INTRODUCTION. 
The object of the present paper is to give the writer’s 
reasons for concluding that all of the volcanic and other 
igneous rocks of any region are so intimately connected 
together by mineralogical and chemical relations that they 
must have originated from some single magma, whose com¬ 
position may be different in different regions; and, further, 
that it is the chemical differentiation of this primary 
magma which has given rise to the various kinds of igne¬ 
ous rocks. 
It is not intended to discuss in this place the physics of 
the interior of the earth, nor the possible cause of volcanic 
activity; but the attempt will be made to present more fully 
than has heretofore been done the petrographical, chemi¬ 
cal, and geological data bearing upon the proposition just 
stated. 
It will he advisable, however, before entering upon this 
undertaking to review the opinions of some of the most 
prominent writers of recent times with regard to this ques¬ 
tion; for “It should be borne in mind,” wrote Von Richt¬ 
hofen in 1868,* “ that among the theories recently proposed 
upon the subjects specified above [namely, the nature, 
origin, and mode of eruption of igneous rocks], there is not 
one which has not already had its prototype in the phantas¬ 
magoria of the time of the dawn of geological science, and 
that it is these which have been constantly reproduced, en¬ 
larged, diversified, remodeled according to the advance of 
science, and supported by continuous accumulation of evi¬ 
dence.” 
It will be seen in the sequel that the writer is only con¬ 
tributing to the establishment of one of the theories which 
was originally conceived with the utmost crudeness, and 
has been gradually assuming greater definiteness and per¬ 
fection. 
*Von Richthofen (F.) “The Natural System of Volcanic Rocks.” 
4°. San Francisco, 1868, p. 47. 
