SCIENTIFIC SUMMARY. 
323 
Space occupied by seven posterior teeth . . . 12*5mm. 
Depth of jaw below last molar ..... 4-4 
Transverse diameter . . . . . . .1*8 
Height of crown of penultimate molar . . .2* 
Transverse diameter . . . . . .1*5 
“ The present specimen indicates an animal about as large as a weasel. It 
is of special interest, as hitherto no Jurassic mammals have been found in 
this country.” — ( Sillimari’s Journal , June 1878.) 
Arctic Geology . — The last British Polar Expedition under Sir George 
Nares hardly satisfied the expectations of the public, but we are gradually 
learning that its scientific results are by no means to be despised. Captain 
Eeilden, the naturalist to the expedition, devoted a good deal of his atten- 
tion to the geology of the region explored, and the fruits of his researches 
add considerably to our knowledge of Arctic Geology. A long paper on 
this subject was read before the Geological Society on April 17, by Captain 
Eeilden and Mr. De Ranee, in which they described the Laurentian gneiss 
that occupies so large a tract in Canada as extending into the Polar area, 
and alike underlying the older Palaeozoic rocks of the Parry Archipelago, 
the Cretaceous and Tertiary plant-bearing beds of Disco Island, and the 
Oolites and Lias of East Greenland and Spitzbergen. Newer than the 
Laurentian, but older than the fossiliferous rocks of Upper Silurian age, are 
the Cape-Rawson beds, forming the coast line between Scoresby Bay and 
Cape Cresswell, in lat. 82° 40'; these strata are unfossiliferous slates and 
grits dripping at very high angles. 
From the fact that Sir John Richardson found these ancient rocks in the 
Hudson’s Bay territory to be directly overlain by limestones containing 
morals of the Upper Silurian Niagara and Onondaga groups, Sir Roderick 
Murchison inferred that the Polar area was dry land during the whole of 
the interval of time occupied by the deposition of strata elsewhere between 
the Laurentian and the Upper Silurian ; and the examination by Mr. Salter, 
Dr. Haughton, and others of the specimens brought from the Parry Islands 
have hitherto been considered to support this view. The specimens of rocks 
.and fossils, more than 2,000 in number, brought by the late expedition from 
Grinnell and Hall Lands have made known to us, with absolute certainty, 
the occurrence of Lower Silurian species in rocks underlying the Upper 
Silurian; and as several of these Lower Silurian forms have been noted 
from the Arctic Archipelago, there can be little doubt that the Lower 
Silurians are there present also. The extensive areas of dolomite of a 
creamy colour abounding in fossils discovered by MUlintock around the 
magnetic pole, on the western side of Boothia, in King 'William’s Island, 
imd in Prince of Wales Land, described by Dr. Haughton, probably 
represent the whole of the Silurian era and possibly a portion of the 
Devonian 
The bases of the Silurians are seen in North Somerset, and consist of 
finely stratified red sandstone and slate, resting directly on the Laurentian 
gneiss, resembling that found at Cape Bunny and in the cliffs between 
Whale and Wolstenholme Sounds. Above these sandstones occur ferru- 
ginous limestones, with quartz grains, and still higher in the series the 
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