MISCELLANY. 



2 SS 



terrible than that of the mouse or of a min- 

 now swallowed by a perch, but there is a 

 repulsiveness about the form, color, and at- 

 titudes of the octopus which invests it with 

 a kind of tragic horror." 



Cooling and Contraction of the Earth's 



Crnst. — Prof. Dana concludes, in the Sep- 

 tember number of the American Journal 

 of Science, a series of able papers on Dy- 

 namical Geology. He states that about 8 

 per cent, is the average change of density 

 for the earth's crust between the stony 

 and liquid states, which is equivalent to 

 a change of volume from 100 to 92 per cent. 

 This, therefore, expresses the contraction 

 or shrinkage which the crust of the earth 

 undergoes in its transition from a liquid 

 condition to that of stone. 



This contraction, as Prof. Dana long 

 since stated, is the source of those inequali- 

 ties of the surface which have resulted from 

 a bending of the earth's solid exterior. 

 From this cause have arisen the elevation 

 of continents and the basin-like depressions 

 now occupied by the waters of the oceans, 

 and from the same cause mountain-chains 

 have been uplifted. 



The origin of the continental eleva- 

 tions and oceanic depressions was when 

 the earth's crust began to form on the fiery 

 liquid mass. Then, from change of den- 

 sity, already noticed, the cooled areas would 

 sink and be overflowed by liquid matter, 

 which, in its turn, would cool. Thus at 

 length a solid and comparatively stable 

 area would result — not elevated as yet, but 

 at the general level of the liquid areas. 

 These would, in their turn, undergo like 

 change of conditions, and a crust, more or 

 less stable, would envelop the globe. This 

 would thicken, by solidifying, underneath 

 the outer shell, as cooling proceeded. 



But in thus solidifying it would undergo 

 a change, both of density and volume, 

 and this change would stand for a certain 

 amount of contraction and subsidence. This 

 amount, by the ratio given, would be in 

 depression to an extent of 5,000 feet, if 

 the crust or rocky layers be 12 miles thick. 

 But the ocean-beds will average in depth, 

 below the mean level of the continents, 

 16,000 feet. In order to effect so great a 

 subsidence, the stony layers must be 38£ 



miles in thickness. In the subsidence sev- 

 eral subordinate dynamical results must 

 occur. One of these is powerful lateral 

 pressure or thrust of the subsiding mass 

 against the more stable areas, and this 

 thrust might be horizontal, or obliquely 

 upward. A consequence of this pressure 

 would be an elevation or yielding, in some 

 form, of the areas against which the pressure 

 was directed. Possibly both have occurred ; 

 certainly the solid crust has bent, until 

 vast mountain uplifts have occurred, and it 

 became fractured to its profound depths. 



From this and other considerations it 

 would appear that continental elevations 

 and oceanic depressions were outlined when 

 the crust began to form, and that they have 

 not since entirely changed places. 



It further appears that the continents 

 are a growth, in which additions to their 

 margins have occurred. Such is evidently 

 the case with the continent of North Amer- 

 ica, as shown in its rocks, in its outlines, 

 and the character and results of its oscilla- 

 tions. 



Improved Deep-Sea Sounding Appara- 

 tus. — In the July number of the Monthly 

 may be found a description of Brooke's 

 self-detaching shot-apparatus for bringing 

 up specimens of the sea-bottom. This in- 

 strument has been considerably improved 

 by Commander Belknap, of the U. S. steamer 

 Tuscarora, now engaged in exploring the 

 bed of the Pacific, with a view to find a 

 suitable berth for a submarine cable from 

 San Francisco to Japan, via the Aleutian 

 Island chain. Commander Belknap's im- 

 provement consists, according to the Engi- 

 neering and Mining Journal, of two cylin- 

 ders, fixed one above the other when the 

 instrument is set and descending through 

 the water, and closing telescopically when 

 the shot is detached on reaching the bot- 

 tom. The lower cylinder is fitted with a 

 conical cup at the lower extremity for the 

 reception of parts of the bottom through an 

 aperture, which, while descending, admits a 

 flow of water upward through the cylinders 

 by means of valves which close hermetically 

 by the pressure of the water when the ap- 

 paratus is being hauled up. The upper 

 cylinder covers the aperture in the lower 

 one on detaching the shot, so that the water 



