THE FOUR PRINCIPAL FAUNAS. 487 



(2.) The Cuboides fauna, with a few species of brachiopods frequent ; 

 other brachiopods rare but occasionally present, and only rarely other 

 classes of organisms. 



(3.) The Goniatite fauna, which is made up mainly of a few species of 

 Goniatites, and when distinct, very little else, but frequently blending with 

 the Cardiola retrostriata fauna, which is a sparse fauna with a few small 

 Goniatites, a few small lamellibranchs, and occasionally Tentaculites and 

 kindred forms. 



(4.) Following this is the upper Devonian fauna of brachiopods and 

 lamellibranchs, the latter often large and of species distinct from those in 

 the middle Devonian. 



With this order of faunas are associated the changes in sedimentation. 

 The first is a calcareous zone formed in an ocean basin not greatly disturbed 

 by shore mud. The second is a deposit of limestone mingled with much 

 clay, showing the waters to have been muddy and impure. The third is a 

 shale, occasionally calcareous, with nodules of limestone, indicating a con- 

 siderable amount of sediment of attrition, but its fineness of division suggest- 

 ing considerable distance from its source. The oscillations in the sedimen- 

 tation of the Devonian system in various places in Europe and America are 

 represented graphically in plate 11.* 



We have here evidence of likeness in the general course of sedimentation 

 for all the central part of northern Europe, through the middle and upper 

 part of what is called the Devonian system. For the northwestern part of 

 the Continent and the southwestern part of England, in south Wales and 

 Cornwall, there is evidence of volcanic disturbances in the middle Devonian. 

 The volcanic disturbances, the stage of oscillations in the relation of the land 

 to the level of the sea indicated by the sedimentation, aud the fossil contents 

 indicative of the stage of biological progress, all agree in indicating uni- 

 formity in the geologic history of this whole region during the period under 

 consideration. It is difficult to conceive any explanation of the facts that 

 does not recognize a comparative contemporaneity for each of the several 

 stages, 1, 2, 3, 4, above named in all its European extent. 



When we pass outside of this north European basin, differences in sedi- 

 mentation are found. In north Devonshire very little limestone appears, 



* Explanation of Plate 11. 



Each diagram is drawn to a uniform scale. The different rulings indicate different kinds of sed- 

 imentation : The right oblique ruling in the vertical columns at the right indicates limestone; the 

 right and left oblique ruling in the middle columns indicates shale or argillaceous deposits; and 

 the right and left oblique ruling with dots in the columns at the left indicates sandstone. The 

 horizontal divisions express geologic divisions of the Devonian system; the lower, middle, and 

 upper divisions standing respectively for the lower, middle, and upper Devonian. 



The heavv curved line is drawn to represent the character of the deposits laid down at each stage 

 of the Devonian in the particular area represented by each diagram. For Instance, figure I repre- 

 sents the sedimentation of north Devonshire: at the bottom the sedimentation curve begins in the 

 sandstone, curves toward the finer deposits, and is in the shales before the close of the lower De- 

 vonian ; in the middle Devonian it is in the shales with an oscillation into the limestone, and then 

 backward it is formed in the sandy shales during the upper Devonian. In the Erbray section, 

 figure 5, the curve begins in sandstone but rapidly runs over to the limestone. The main part of 

 the lower and all the middle Devonian are limestones. 



