GEOLOGY. 335 



Chazy, and Calciferous, tbe beds of the latter yielding an abundant and 

 remarkable fauna. The strata are here affected by several folds, some 

 of them involving even the newest strata, and generally have a steep 

 easterly dip. Recent observations by Dwight show a direct superpo- 

 sition of Trenton upon the Calciferous, probably unconformably, as is 

 seen elsewhere in the valley, where the Trenton lies upon the slates of 

 the so-called Quebec group. The greater portion of this latter doubtless 

 belongs to a series which includes the typical Calciferous as a stage, but 

 the stratigraphical relations of the latter, as seen near Poughkeepsie, to 

 the Cambrian slates remain to be determined. 



Marr has lately studied the lower Paleozoic rocks of Bohemia, where he 

 found the stages B and C of Barrande to rest unconformably upon stage 

 A, the latter being composed of crystalline rocks, which Marr compares 

 with the Pebidian of Wales (Huronian) ; B he considers to represent 

 the Harlech beds, at the base of the Welsh Cambrian, while C and D 

 are equivalent to the Lingula flags and the Tremadoc, followed, how- 

 ever, by representatives of the Arenig and Bala. These divisions thus 

 include representatives of the first and second faunas of Barrande, 

 while the succeeding stages B and F contain his third fauna. It is 

 in D that are found, according to Barrande, what he described as 

 " colonies " of the third fauna, which he supposed had existed there con- 

 temporaneously with the second fauna. Marr, however, after detailed 

 stratigraphical studies, considers these apparent associations to be due 

 entirely to physical disturbances, or, in other words, that they are to be 

 explained by faults and folds by which the younger have been involved 

 in the older strata. 



Marr has also discussed the question of nomenclature and classification 

 of the lower Paleozoic rocks, in opposition to the views of Barrande, and 

 in supi3ort of the use of the term Cambrian in its original and historic 

 sense. The difficulties in the way of arriving at a general application of 

 the term Cambrian to the upper division of Sedgwick's system, which 

 Murchison, by a mistake in stratigraphy, included in his Silurian, are, 

 however, so great that its general adoption seems impossible, and it is 

 to meet this state of things that the distinctive term Ordovician or 

 Crdovian has been proposed for this division of the lower Paleozoic 

 rocks. 



Lai) worth, in the Geological Magazine for June and July, 1S81, has 

 made a detailed comparison between the lower Paleozoic rocks of Great 

 Britain and Scandinavia, and Schmidt has done the same for the Baltic 

 provinces of Eussia. 



CLASSIFICATION OF EOZOIO AND PALEOZOIC KOCKS. 



For the better understanding of the nomenclature of the great sub- 

 divisions of the Eozoic and lower Paleozoic rocks referred to in the 

 preceding pages, a brief summary is subjoined, numbered in ascend- 

 ing order. 



