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IIARDWICKE'S SCIENCE-GOSSIP. 



probably 1,000 ft., the deposits formed in this 

 containing the third or " Menevian " fauna. This 

 depression enabled the water to spread over the 

 area between the south of Prussia and Bohemia and 

 Norway and Sweden, there being no evidence of 

 the presence of the first and secoud faunas over 

 this area. The filling up of this depression led to 

 the deposition of the shallow-water deposits of the 

 Lingula-flag group, followed by. another sudden 

 depression at the commencement of the Tremadoc 

 epoch, which allowed the water to spread freely 

 over the whole European area. The author next 

 discusses the faunas of the successive epochs, and 

 indicates that these are also in favour of his views. 

 He indicates the probability that the animals, which 

 are all of marine forms, migrated into the European 

 area from some point to the south-west, probably 

 near the equator, where he supposes the earliest 

 types were developed. Both the lower and higher 

 types of invertebrates appear first in the western 

 areas; and the groups in each case as they first 

 appear are those which biologists now recognize 

 as being most nearly allied, and which may have 

 developed from one common type. The lower 

 invertebrates appear at a very much earlier period 

 than the higher in all the areas. In the "Welsh 

 area the higher forms (the Gasteropods, Lamelli- 

 branchs, and Cephalopods) come in for the first 

 time in Lower Tremadoc rocks; aud with the 

 exception of the presence of a Gasteropod in rather 

 lower beds in Spain, this is the earliest evidence 

 of these higher forms having reached the European 

 area. At this time, however, no less thau five 

 distinct faunas of lower invertebrates had already 

 appeared; and an enormous period, indicated by 

 the deposition of nearly 15,000 feet of deposits, 

 had elapsed since the first fauna had reached this 

 area. The author points out also that a similar 

 encroachment of the sea and migration of animals 

 in a north-westerly direction occurred in the North 

 American area at about the same time, the lines 

 indicating the European and American depressions 

 meeting in mid- Atlantic. 



"On the Superficial Geology of the Cen- 

 tral Region of North America."— This was a 

 paper read at the same meeting by G. M. Dawson, 

 Esq., Assoc. B.S.M., Geologist to H.M. North 

 American Boundary Commission. Physical geo- 

 graphy of the region. — The region under considera- 

 tion is that portion of the great tract of prairie of 

 the middle of North America from Mexico to the 

 Arctic Sea, which lies between the forty-ninth and 

 fifty-fifth parallels, and extends from the base of the 

 Rocky Mountains to a ridge of Laurcntian rocks 

 that runs north-west from Lake Superior towards 

 the Arctic Sea, and is called by the author the 

 " Laurentian axis." This plateau is crossed by two 

 watersheds ; one, starting from the base of the 



Rocky Mountains at about the forty-ninth parallel, 

 runs, due east to the 105th meridian, when it turns 

 to the south-east, dividing the Red River from the 

 Missouri ; the other crosses from the Rocky Moun- 

 tains to the Laurentian axis near the fifty-fifth 

 parallel. The whole region between these two 

 transverse watersheds slopes gradually eastward, 

 but is divisible into three prairie steppes or plateaus 

 of different elevations. The lowest includes Lake 

 Winnipeg aud the valley of the Red River ; its 

 average alti'ude is 800 feet. The second, or the 

 " Great Plains," properly so called, has an average 

 elevation of 1,600 feet. The third or highest is 

 from 2,500 to 1,200 feet above the sea, and is not 

 so level as the other two. Glacial phenomena of the 

 Laurentian axis. — The neighbourhood of the Lake 

 of the Woods is taken by the author as furnishing 

 an example of the glaciation visible in many parts 

 of the Laurentian axis. This lake is seventy miles 

 long, and has a coast line of three or four hundred 

 miles. The details of its outline closely follow the 

 character of the rock, spreading out over the 

 schistose and thinly-cleavable varieties, and becom- 

 ing narrow and tortuous where compact dioritic 

 rocks, greeustone, conglomerate, aud gneiss prevail. 

 The rocks, both on the shores and the islands in the 

 lake, are rounded, grooved, and striated. The 

 general direction of the striae is from north-east to 

 south-west. Drift plateau of Northern Minnesota 

 aud Eastern Manitoba. — This plateau consists of a 

 great thickness of drift deposits, resting on the 

 gently-sloping foot of the Laurentian, aud is com- 

 posed, to a depth of GO feet or more, of fine sands 

 and arenaceous clays, with occasional beds of gravel 

 and small boulders, probably reposing throughout 

 on boulder-cky. The only fossil found was a piece 

 of wood apparently of the common cedar.](2'/foyV< 

 occidentalis). The surface of the plateau is strewn 

 with large erratics, derived chiefly from the Lauren- 

 tian and Huronian to the north ; but there are also 

 many of white limestone. The fossils in some of 

 the latter being of Upper Silurian age/^the author 

 is inclined to believe, with Dr. Bigsby, that an out- 

 crop of Upper Silurian is concealed by the drift 

 deposits in the Lake of the Woods region. Lowest 

 prairie level and valley of the Red River. — This 

 prairie presents an appearance of perfect horizon- 

 tality. The soil consists of fine silty deposits, 

 arranged in thin horizontal beds, restiug on till or 

 boulder- day. Stones were exceedingly rare. The 

 western escarpment was terraced and covered with 

 boulders. It is therefore probable that this prairie 

 is the bed of a preglacial lake. The second prairie 

 plateau is thickly covered with drift deposits, which 

 consist in great part of local debris, derived from 

 the under -lying soft formations, mixed with a 

 considerable quantity of transported material, es- 

 pecially in the upper layers. Large erratics are 

 in places abundant ; they consist mainly of Lauren- 



