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 



