PROGRESS IN THE STUDY OF ANCIENT SEDIMENTS. 3 



tract at Loch Maree not improbably represents the Upper 

 Laurentian or Grenville series, and this certainly occurs in 

 the western islands. . . . The Torridon sandstones and 

 the associated beds . . . seem ... to be equivalent to 

 the Huronian of Logan. . . . The Uriconian and Long- 

 myndian of Geikie probably include the equivalents of our 

 Kewenian, and the same may perhaps be said of the Dal- 

 radian of Scotland. . . . Some portions of these rocks may, 

 however, be the same with what in Canada has been called 

 by Matthew ' basal Cambrian '." Without commenting 

 further on the vexed question of the correlation of the 

 Precambrian rocks of different areas, which will remain 

 in a state of uncertainty until far more work has been 

 done amongst the rocks, we may pass on to notice a 

 sentence occurring in Sir William's criticism of the theories 

 of coal-making : " The coal-deposits of the great Carboni- 

 ferous system . . . mark a special stage in the production 

 of our continents, when they were less differentiated as to 

 orography, and when a very uniform and equable climate 

 extended over the northern hemisphere accompanied by a 

 very peculiar vegetation. Such conditions did not occur in 

 combination and to a like extent in any succeeding period 

 in the earth's history." This sentence contains a note of 

 warning which some writers will do well to consider. Ex- 

 treme uniformitarians sometimes appear to forget that in 

 every system, differentiation has proceeded to a greater 

 extent than in the preceding one, and that as with the 

 Carboniferous so with the other systems, the conditions 

 do not "occur in combination, and to a like extent in 

 any succeeding period ". 



Having passed over the Atlantic we may pause there 

 before returning to the Old World to notice two papers 

 treating of kindred subjects, the occurrence of certain con- 

 glomerates amongst the Palaeozoic rocks. The first of 

 these treats of " Palaeozoic Overlaps in Montgomery and 

 Pulaski Counties, Virginia" (3). 



The rocks described in this paper are in ascending 

 order : — 



1. Cambrian. The Graysonton Formation, a mass of 



