400 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



elements were in a state of softness, which permitted the union of these hetero- 

 geneous ))odies to form a solid mass. Moreover this aggregation cannot be 

 supposed to have been formed after the last cast of the primordial deposit, be- 

 cause the rents, which took place in its mass, have been filled by veins or 

 rather strata of amphiboloid and felsparoid .... wlaich demonstrates, that 

 these minerals were still depositing themselves, at a period later than the for- 

 mation of the wacke." 



The amygdaloidal basalt (nielapliyr) was called amygdaloid, and re- 

 garded as made up of nodules cemented by an apparently homogeneous 

 reddish-browu or greenish substance. It is said that 

 " sometimes it occurs with a schistous texture, and even emits an argillaceous 

 smell, when breathed on. This rock is analogous to the toadstone of the Eng- 

 lish." 



In Godon's work is seen the same theoretical belief in the passage 

 of one rock into another which has since his time played so important 

 a factor in the geological papers in this region, all resting, however, on 

 theory and imperfect observation. 



Next in order followed Mi\ William Maclure's paper, entitled " Ob- 

 servations on the Geology of the United States, explanatory of a Geo- 

 logical Map," (Trans. Am. Phil. Soc, 1809, VL, pp. 411-428,) which 

 was followed by an enlarged .paper on the same subject in 1817. 

 (Ibid., 1818, (2) I., pp. 1-91.) The latter paper was also published' 

 as an independent work in 1817. Maclure, following Werner, arranged 

 all rocks in four classes : Primitive, Transition, Floetz or Secondary, 

 and Alluvial Rocks. 



Dr. Hunt in his History of the Azoic Rocks (Second Geological Sur- 

 vey of Pennsylvania, 1878, E., Part I. pp. 23, 24) fell into the error of 

 maiking Maclure's classes of rocks five in number. This was done by 

 Dr. Hunt's placing the " Old Red Sandstone'" as a distinct class, al- 

 though Mr. Maclure regarded it as belonging to the Floetz or Secondary 

 class, being one of the twelve formations into which that class was 

 divided. Dr. Hunt's mistake probably arose from the fact that the 

 " Old Red Sandstone " (Mesozoic) of Maclure was colored distinctively 

 on the map, which was the case with all the classes, but not with the 

 other formations. This rock was furthermore placed at the base of the 

 Secondary, and regarded as making a passage from the Transition to 

 the Secondary classes. 



The rocks in the vicinity of Boston were placed by Maclure in the 

 Primitive and Transition classes. The Transition corresponded gener- 

 ally with the conglomerate in this region, and it was directly connected 

 with the Rhode Island Coal Basin, then regarded as Transition. 



