xcviii GENERAL SUMMARY OF SCIENTIFIC AND 



CRYSTALLINE LIMESTONES. 



Hall finds that certain serpentinic limestones of the region are 

 newer than both of these series, which they overlie unconformably, 

 including at the same time fragments derived from the gneisses. 

 That crystalline limestones containing serjDentine and various other 

 minerals do, however, form portions of the Laurentian series in Can- 

 ada is undoubted, but it by no means follows that all such crystalline 

 limestones belong to this horizon. Hunt has pointed out that lime- 

 stones, much resembling in mineralogical characters those of the 

 Laurentian, occur in the Montalban of New England, and also, as 

 noticed above, that serpentinic limestones are found in the Lower 

 Taconic rocks of Pennsylvania. These facts give an additional in- 

 terest to the imjDortant observations of Hall, Some late researches 

 of Vennor in the province of Ontario tend to similar conclusions. 



THE QUEBEC GROUP OR UPPER TACONIC. 

 The fauna of the Lower Taconic rocks in Pennsylvania is scarcely 

 known, but in addition to a Scolithus, which differs from that of the 

 New York Potsdam, Prime has made known the existence of an 

 undetermined linguloid shell, and also of impressions similar to the 

 Monocraterion found by Torell in the lowest Cambrian beds of Swe- 

 den, Referring to the lower divisions of Paleozoic time. Hunt has 

 again called attention to the fact that the so-called Quebec group 

 of Logan (the Upper Taconic of Emmons) was based ujion an in- 

 verted succession of strata on an overturned anticlinal. The slates 

 with compound graptolites, of the Levis division, which were repre- 

 sented by Logan as inferior to the Levis limestones, are of the age 

 of the Skiddaw or Arenig rocks, while the limestones themselves 

 are the equivalents of the Tremadoc division of Great Britain. The 

 Sillery, which was regarded as the summit of the Quebec group, is 

 much lower, and probably of Menevian age. In the province of 

 Quebec it rests in some localities on the crystalline schists of Hu- 

 ronian age, which were supposed by Logan to be the Levis and the 

 overlying Lauzon division in an altered condition, although the Levis 

 rocks are now shown by their fauna to belong to the upper part of 

 the series, and contain fragments of these same crystalline schists. 



CRYSTALLINE ROCKS OF SCANDINAVIA. 

 Pettersen has described the crystalline rocks of Northern Norway 

 as including an older series of red and gray gneisses, often horn- 

 blendic, with micaceous and hornblendic schists and much crystalline 

 limestone. These are overlaid by a series of argillaceous and horn- 

 blendic rocks, with gabbro (diorite or diabase) olivine-rock, serpen- 

 tine and steatite, and associated copper and nickel ores. Related 

 strata are described by him as a series of many-colored argillites, 



