14 
At the time the work on the Cordilleran collections began, 
“The Natural System of’ Volcanic Rocks” of Richthofen, and 
“ The Microscopical Petrography ” of the Fortieth Parallel Sur- 
vey, were generally accepted as guides to the lithology of more 
recent volcanic rocks occurring in this country, as well as the 
older eruptive ones. But as Dr. Wadsworth’s investigations 
progressed, it became evident that Richthofen’s system was 
defective in its basis, as well as too limited in its scope to be a 
satisfactory guide in arranging the Cordilleran rocks. More- 
over, it appeared, on carefully examining the collections of the 
Fortieth Parallel Survey and Professor Zirkel’s work thereon, 
that this work was replete with errors of detail of the gravest 
character ; while its leading ideas, although in large part iden- 
tical with those of Richthofen, were at the same time decid- 
edly less philosophical in character. These facts required an 
abandonment of the Fortieth Parallel results; although such 
material furnished by that survey as was of value could be 
freely used in endeavoring to arrive at a more satisfactory 
classification. 
The results obtained by Dr. Wadsworth, so far as reached at 
that time were published by him in 1879, in the Bulletin of the 
Museum, under the title of “ A Classification of Rocks.” This 
paper led to much caustic public and private criticism, as well 
as efforts to interfere with the further prosecution of the inves- 
tigations. These criticisms, and the answers thereto, will be 
found in various papers published in the Proceedings of the 
Boston Natural History Society, from 1881 on. 
The work of the geologists and lithologists of the United 
States Geological Survey, quite recently published, however, 
sustains in a remarkable manner the conclusions formulated in 
Dr. Wadsworth’s * Classification of Rocks”; although — owing 
to the bitterness engendered at the time of the first publication 
of that paper, when it was almost universally believed to be 
false in its conclusions, as it was most decidedly in conflict with 
the results obtained by two learned and able German professors — 
the later investigators in this field have not acknowledged the 
priority of Dr. Wadsworth’s work, or given due credit to the 
Museum for the important results attained under its auspices. 
While, in carrying on the task thus undertaken, the same 
general direction of thought has been followed of which the 
a 
