ST.joHx.l PALAEOZOIC AREAS NIAGARA. 485 



characteristic Upper Silurian corals. The rock in this region is pretty 

 miifomily a heavy-bedded, light to dirty buff, in places reddish-stained, 

 magnesian limestone, attaining a thickness of from 400 to 000 feet. 

 Wherever erosive action has laid it bare, as in the canon sides and great 

 promontories overlooking the Alpine basins in the heart of the range, 

 it presents peculiarly characteristic exposures, picturesque castellated 

 cliff's, and massive foundation walls which support the more fragmentary 

 superimposed Carboniferous deposits. In many of its features, even the 

 peculiar rough pitted manner of weathering, and its porous or minutely 

 vesicular structure, it strongly recalls the Niagara magnesian beds, whose 

 bluff exposures form some of the most picturesque scenery along the 

 shores of the Upper Mississippi. 



The same deposit appears in the Gros Ventre Mountains, where it also 

 maintains about the same thickness. In the Buffalo Fork Peak uplift, 

 however, it is greatly attenuated, if indeed it at all exists. At Station 

 XLIX, in the latter region, a vertical space of about 200 feet intervenes 

 between the uppermost layers of the Quebec limestone and the summit 

 of the station, and which is filled by gray, reddish-stained, cherty lime- 

 stones, the summit ledges and a hundred feet below holding characteristic 

 Carboniferous fossds. There are no indications of nonconformity be- 

 tween any of the above-mentioned deposits at this locality, and the ap- 

 pearances point to the conclusion that the deposition of calcareous or 

 limestone-making sediments was uninterrupted from the commencement 

 of the upper limestone of the Quebec to the Carboniferous. The litho- 

 logical distinctions between the Quebec and the overlying limestones are 

 sharply drawn, while the immediately superimposed limestone layers do 

 not differ in any marked degree from the higher layers containing Car- 

 boniferous fossils ; so that if they do belong to the Niagara period, they 

 were not affected by or did not participate in the transformation which 

 elsewhere converted the entire horizon into a dolomitic deposit. 



CARBONIFEROUS. 



Eocks of the age of the Carboniferous are extensively developed in 

 the district, constituting a most important element in the stratigraphy 

 of its orographic reliefs ; indeed whole mountain ranges are carved almost 

 entirely out of deposits pertaining to this age. A generalized section of 

 these rocks falls into two categories or great divisions, viz, Lower and 

 Upper Carboniferous, the persistency of which may be considered as 

 being more or less well established. The great divisions, or periods, 

 seem to be further divisible into what may prove to be more or less well- 

 defined subdivisions, which may in part correspond to the epochs which 

 marked the various life stages of these periods in other regions. Although 

 it has not been possible to define the limits of these lesser divisions, or 

 to establish the relations of the fauual assemblages contained therein to 

 those which characterize definitely determined horizons in rocks of this 

 age in longer known and more thoroughly studied localities, at least 

 some evidence, which seems to point to their existence in reality, has 

 been observed, so that their general outlines may be stated with a de- 

 gree of confidence. Such as they were found to be, within the limits of 

 the present district, are briefly sketched in the following pages. 



Lower Carboniferous. — The time of the inferior division of the Carbon- 

 iferous was eminently a limestone-making period, with, however, infu- 

 sions of siliceous matter, which became seggregated mainly in the form of 

 chert, in both nodules and layers, with occasional heavier siliceous de- 

 posits or quartzitic sandstones. The local lithology and chemical char- 



