270 PRINCIPLES OF STRATIGRAPHY 



exogenetic divisions used in this book. Naumann's terms have been 

 adopted in the latest of French text-books by Hang (14), but in a 

 more restricted meaning. He, first of all, divides all rocks into roclies 

 exogcnes, or those formed on the outside of the earth, i. e., the sedi- 

 mentary rocks ; and into the roches endogcnes, or those having their 

 origin from within the lithosphere, i. e., the volcanic rocks. The exo- 

 gene rocks are then divided into roches protogcnes, comprising (a) 

 the chemical and (b) the organic deposits, and roches deutogcnes, or 

 the elastics. The old notion of a primary distinction between igne- 

 ous and sedimentary rocks still prevails in this classification, but 

 Haug recognizes the important distinction between elastics and non- 

 clastic sediments. Zirkel (31), too, used similar subdivisions of 

 primary rank when he divided rocks into : A, Original crystalline, 

 and B, Clastic rocks ; terms used by Naumann in the first edition 

 of his Lehrhuch, 1850. The term for the first group was not well 

 chosen, since it included rocks which were not crystalline. /. e., ob- 

 sidian, etc. For this reason Zirkel substituted the term non-clastic 

 in 1873. Both Naumann and Zirkel included metamorphic rocks in 

 their class of Protogene or non-clastic (crystalline) rocks.- H. 

 Rosenbusch (24), in 1877, on the other hand, included metamor- 

 phic rocks in his class of stratified rocks (Gcschichtete Gesteine), 

 which, with the class of massive rocks (Massige Gesteine) — the 

 igneous rocks of our present classifications — constituted the two ma- 

 jor divisions of rocks. In 1898 (25), however, he made the three fol- 

 lowing classes: I, Eruptive rocks (Eruptivgesteine). These are 

 the igneous rocks of other authors and they are divided into : a, 

 deep-seated rocks, or Tiefengesteine (Plutonic rocks of other classi- 

 fications) ; b, dike rocks, or Ganggesteine ; and, c. efifusive rocks, or 

 Ergussgesteine, i. e., volcanic rocks of later classifications. II, 

 Stratified rocks (Schichtige Gesteine). These include clastic sedi- 

 ments and chemical precipitates from water; rocks of organic 

 origin and the porphyroid rocks. The latter, though bedded, are 

 clearly out of place in this division, as the author himself recognizes, 

 since they never were sediments nor are such now, but are meta- 

 morphic derivatives of igneous rocks. Siliceous rocks of organic 

 (biogenic) and those of aqueous (hydrogenic) origin are grouped 

 together by Rosenbusch in this classification, and the same is true 

 for calcareous rocks. Coals and other combustibles are placed in 

 a separate subdivision or appendix. Under argillaceous rocks are 

 included the phyllites and other more, or less altered or metamor- 

 phosed clay rocks ; under sandstones he includes quartzites, and 

 under calcareous rocks he places marbles, but other metamorphic 

 rocks are placed in the third main division. Altogether the grouping 



