400 



THE AZOIC SYSTEM AND ITS SUBDJ VISIONS. 



elementB were in a state of softness, wliicli permitted the union of the?;e hetero- 

 geneous hodies to forni a solid nia.ss. Moreover []us a^'gregalion canm.it he 

 sn[)posed to have l)een formed after the last cast of the primordial deposit, he- 

 cause the rents, whicli took place in its mass, have heen filled hy veins or 

 rather strata of ampldholoid and I'elsparoid .... vhich demonsti'ates, t]iat 

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

 mation of the Avacke." 



The amygdaloidal basalt (n:iclapliyi-) was called amygdaloid, and re- 

 garded as made up of nodules cenieuted by an apparently honiogeneoua 

 reddish-brown or greenish substance. It is said that 



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



smell, when breathed on. 



bsh." 



This rock is analogous to the toadstone of the Eug- 



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

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

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

 theory and imperfect observation. 



Next in order followed Mr. William Maelure's paper, entitled *' Ob- 

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

 logical Map,^' (Trans. Am. PhiL Soc, 1809, YL, pp. 411-428,) which 

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

 (U)id., 1818, (2) L, pp. 1-01.) The latter paper was also published 

 as an indcj^endent work in 1817. Maclure, following Werner, ai-ranged 

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



and Alluvial Iloeks. 



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

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

 making Maoliu'c's classes of rocks five in luimbor. This was done by 

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

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

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

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

 '' Old Ped Sandstone " (Mesozoic) of Maclure was colored distinctively 

 on the map, whicli was tlie case with all the classes, but not wdth the 

 of/'cr forinations. 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 tlie conglomerate in this region, and it was directly connected 

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



[, 



