GEOLOGY. 245 



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

 boniferous); on the Mesozoic, (1. J I. (^ook ; on tlie (Irnozoii^, l). A. 

 Sniitli (marine Cenozoic), and \j. I). Co)ie (interior Cenozoic) ; and on 

 tlie ((Quaternary and recent, C. II. Hitcli(;ock. 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- 

 tication or classilication 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 iu current thought awakened through the or- 

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

 American Association at New York in 1887, Gill)ert developed certain 

 fundamental considerations iu 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 

 pur[)oses; e. (/., the mining geologist may only be interested in the 

 structural classification, while the paleontologist or student of geo- 

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

 say that this address elicite<l adverse criticism, Jiotably 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 cartography in use by the IT, S. (Jeological Survey in 1885 was 

 ]>resented before the Congres Geologique International at Berlin 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 ai)peared. 



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

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

 mation already in hand, but also in much valuable work in the fi(^ld; 

 and the outcome of this work comprises several of the most im[)ortant 

 contiibutions to geologic progress made during the last two years. 



Foremost among these must be ])laced 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 

 <!rystalliiu^ nucleus which everywhere forms the fouiulation upon which 

 the clastic strata ar«>: built. This lu'wly-recognized series of ro(;ks is 

 best developed in tiie Lake Sujjcrior region, where it was studied by 

 Irving and his associates ; l>ut apparent equivalents have been found in 



"Am. Naturalist, vol. xxi, pp. Hll, 847, aiwl olHowbore. 



