NATURE OF THE ROCKS. 3i3 



likewise the case on tlie Tschukutskoi coast, as the 

 specimens brought from tlicnce contain white- 

 grained calcareous stone sprinkled with silver-white 

 mica, and graphite is also found in the neighbour- 

 hood, which generally belongs to the mica slate. 

 Of the kind of rock itself, we have a specimen 

 from Kotzebue's Sound, lying opposite, where it 

 may be found in the neighbouring mountains. 

 The mica is silver-white, like that which the lime- 

 stone contains; may not, therefore, the hypothesis 

 be allowed, that the primitive rock continues from 

 Asia to America, and that both continents were 

 once united at Beering's Strait ? As the one 

 coast (the Asiatic) is said to be steep, the opposite 

 one flat, they are to each as the banks of a river 

 and side valleys, forming by running waters. The 

 supposition of a later separation is therefore not 

 contradicted by the natiue of the strait. 



No direct observation has informed us what kinds 

 of rock occupy the space between Beering's 

 Strait and the Aleutian islands ; but as on the north 

 side of Oonalashka a layer of gneiss syenite was 

 found, and in Kotzebue*s Sound a very remarkable 

 porphyritic syenite, these formations may perhaps 

 serve as a basis for the floetz mountains of the 

 Aleutians. In this case the extended basin be- 

 tween the above mentioned island-chain and New 

 California, appears to be an inlet bounded by two 

 groups of primitive rock, and filled with floetz 

 rock, whose similar formations (sand-stone, conglo- 



z 4< 



