183 



both at the water's edge and on the summits of the most elevated 

 hills. Those in the bays, as at Green Bay, were nearly all situ- 

 ated near the low water mark, and may doubtless have been 

 drifted in by the floating ice which makes its appearance on the 

 coast every spring ; but a different explanation must be given to 

 account for those on the elevated rocks and hills. Nearly all the 

 protruding rocks are rounded and the marks known as " Drift 

 marks," "Diluvial scratches," and " Glacier marks," existed in 

 great abundance. The smooth and rounded rocks are especially 

 observable at Bras d'Or. They are all rounded on the northern 

 side. 



Prof. Agassiz remarked that in Cambridge, on the road 

 to Mount Auburn, there may be seen at the present time, 

 in a recently opened gravel-pit, an instance of the two 

 kinds of drift, one above the other. The upper one is of 

 marine and the lower of glacial origin. The former is 

 made up of diflferent materials, distinctly stratified, and 

 exhibits marks of tidal action, but contains no boulders. 

 The lower one consists of small and large pebbles, more or 

 less scratched, irregularly scattered through a bed of mud. 



Dr. Cabot stated, that at Deer Island, in Boston Harbor, 

 a similar drift deposit may be seen. 



Mr. Girard read a paper on the genus Cottus. 



ON THE GENUS COTTUS Auct. 



There are in the genus Cottus^ as it has hitherto been admit- 

 ted, two groups of species always very easily distinguished from 

 each other at first sight ; the head of the one is smooth or nearly 

 so ; that of the other is tuberculous, or armed with spines ; the 

 former inhabits fresh water, the latter salt or brackish water at 

 the mouths of rivers. 



These two groups are generically distinct both by external 

 characters and anatomical structure. It remains only to decide 

 which should retain the name of Cottus, and to which it will be 

 necessary to give a new name. 



The most simple way to settle this question, will be to go back 

 to the origin of the genus Cottus and follow its history. 



