GEOLOGY. 245 



Upper Paleozoic, 11. S. Williams (Devonian), and J. J. Stevenson (Car- 

 boniferous); on llic Mesozoic, G. H, Cook; on tiie Cenozoic, E. A. 

 Smith (marine Cenozoic), and E. D. Cope (interior Cenozoic) ; and on 

 the Quaternary and recent, C. H. Bitchcock. The several reports were 

 edited and prefaced with a history of the committee by Frazer, printed 

 in an octavo volume of about 250 pages, and distributed at the London 

 session of the Congres Geologique International. It should be ob- 

 served that these reports, and the general system into which they are 

 designed to be thrown, generally represent the primitive analytic classi- 

 fication or classification by products, and not the synthetic classification 

 or classification by genesis, mentioned in an earlier paragraph. 



The formal reports of the American committee represent however 

 but a part of the activity in current thought awakened through the or- 

 ganization of the Congres. In his vice-presidential address before the 

 American Association at New York in 1887, Gilbert developed certain 

 fundamental considerations in geologic taxonomy, nomenclature, and 

 cartography. The address brought out clearly the distinction between 

 classifications based upon structural units, and upon time units respect- 

 ively — classifications which may be perfectly distinct, though both may 

 traverse the same ground and which are both valuable for different 

 purposes; c. </., the mining geologist may only be interested in the 

 structural classification, while the paleontologist or student of geo- 

 chrony may be interested only in the time classification. It is just to 

 say that this address elicited adverse criticism, notably by Frazer.* A 

 year later Vice-President Cook addressed his section of the American 

 Association at Cleveland on a similar subject. A statement of the meth- 

 ods of cartograph}' in use by the U. S. Geological Survey in 1885 was 

 l)resented before the Congres Geologique Intern;itional at Berlii^ in 

 that year by McGee, and was published in 1888 in the compte rendu of 

 the session ; and other contributions to the taxonomy of the clastic rocks 

 have appeared. 



It is to be noted that the interest awakened by these discussions re- 

 sulted not only in much writing on geologic taxonomy based upon infor- 

 mation already in hand, but also in much valuable work in the field; 

 and the outcome of this work comprises several of the most important 

 contributions to geologic progress made during the last two years. 



Foremost among these must be placed the recognition by Irving and 

 his associates (Chamberlin and Van Ilise) of a vast mass of sediments, 

 nearly G miles in vertical thickness, below the base of the previously 

 known fossiliferous rocks of the terrestrial crust and above the original 

 crystalline nucleus which everywhere forms the fouiulntion upon whicli 

 the clastic strata, are built. This newly-recognized series of rocks is 

 best developed in the Lake Superior region, where it was studied by 

 Irving and his associates; but apparent equivalents have been found iu 



*Am. Naturalist, vol. xxi, pp. H41, Ht7, an<l olsewliere. 



