530 



SCIENCE. 



[N. S. Vol. XXII. No. 565. 



organic rock in which all organic structure 

 has been obliterated. Personally, I prefer 

 terms derived from the Latin as being more 

 adaptable in composition in this instance than 

 the Greek terms of ISTaumann and Hauy; but 

 whether we say calcopsephyte, calcopsammyte 

 and calcopelyte or calcirudyte, calcarenyte and 

 <?alcilutyte, is of minor significance, so long 

 as we employ a term which will express ex- 

 actly the physical characters of the rock. If 

 the name at the same time expresses, in part, 

 the history of the rock, by indicating it to be 

 a clastic and not an organic rock, this can 

 only be regarded as a further advantage. Cer- 

 tainly, if you understood that a lutyte was a 

 clastic rock composed of fine rock flour, you 

 would, I think, be in favor of describing many 

 of the beds of the Manlius and water-lime of 

 this region as argillaceous calcilutytes or pure 

 calcilutytes, as the case may be, rather than 

 to speak of them as : ' compact, finely-bedded 

 argillaceous limestones with conchoidal frac- 

 ture and of an impalpable grain.' I should, 

 at any rate; for, if nothing more than brevity 

 is gained, the short term is a distinct ad- 

 vantage. 



But the application of a more precise 

 nomenclature to the clastic rocks is only a 

 first step in the right direction. The lithic 

 -character of the rocks must be studied with 

 reference to their origin, i. e., the lithogenesis 

 of the formations must be considered, and the 

 bearing which this has on the distribution of 

 land and sea in past geologic epochs. The 

 careful study of local sections, the measure- 

 ments of thicknesses and the determination of 

 the distribution of fossils, are of course, an 

 important preliminary. But while this is 

 done, a careful diagnosis of the lithic char- 

 acter of the rock and a determination of its 

 source should be made, and special care should 

 be given a precise description of its rela- 

 tionship to adjacent formations. The latter 

 feature is too often neglected, when it is of 

 the greatest importance, as an example will 

 show. Most of the descriptions of the Chat- 

 tanooga black shale which I have been able to 

 find speak of it as a black bituminous shale, 

 with some few additional remarks on its 

 ;petrographic character. They mention the 



fossils which are found in it and refer the 

 formation to the Devonic, with sometimes a 

 more precise reference to the Marcellus or the 

 Genesee of New York. But its relation to 

 the succeeding formation is almost never dis- 

 cussed. Here and there in the literature we 

 find a hint, and only a hint, that it grades up 

 into the overlying rock. Rarely is there a 

 more precise description of this gradation, 

 like William's description of its relation to 

 the overlying Grainger shale. And yet this 

 is of very great importance, for if the Chat- 

 tanooga shale of eastern Tennessee is Devonic, 

 then there is not only a pronounced hiatus at 

 its base, but another at its top, for the im- 

 mediately overlying Fort Payne beds represent 

 in some localities the' St. Louis, in other the 

 Keokuk. In still other localities we find beds 

 of Chester age following immediately upon 

 the black shale, which often is only a few feet 

 thick, while in other localities again these 

 black shales are succeeded by beds of Burling- 

 ton or Kinderhook age. If, as I strongly 

 suspect, and as seems to be occasionally hinted 

 at in the literature, there is no hiatus at the 

 top of the black shale, but a transition to the 

 ■ overlying formation, then the black shale 

 surely represents the basal formation formed 

 by a sea transgressing southward and eastward 

 over a peneplained land surface, and its age 

 varies in different localities. At the type 

 locality, Chattanooga, Tennessee, the age of 

 the black shale is in that case Burlington or 

 perhaps early Koekuk, while at others its age 

 is St. Loiiis, or even later. Only in the north- 

 ern region, where it is succeeded by Kinder- 

 hook beds, as at New Albany, Indiana, and at 

 Big Stone Gap, Virginia, is the black shale of 

 Devonic age. 



And this brings me to the consideration of 

 another factor which is all too often over- 

 looked in stratigraphic work. This is the 

 phenomenon of progressive overlap, and the 

 complementary one, which, for lack of a better 

 term, we may call regressive overlap. We all 

 agree that in normal sedimentation coarse 

 clastic rocks are formed near shore, finer far- 

 ther out and the finest impalpable flour is only 

 deposited at a great distance from the nor- 

 mal shore, while clastic limestone may be 



