498 LTE JOURNAL OF NGLOLOGN. 
east are comparable with those occupying the interior of the plateaus. 
The descent of the canyon of the Colorado alone cannot be taken, but 
that of the reaches of the canyon and of the valley to where it emerges 
on the highlands of the Great Basin at an elevation of 7000 or 8000 
feet. The descents of these valleys are not appreciated by their mean 
slopes, which in part are insignificant but in other places they are pre- 
cipitous. It is necessary to analyze the details. Thus the writer has. 
observed the descents of the existing land valleys through thousands 
of feet with characters and slopes\comparable with those sunken across. 
the sunken coast plains. This study will be brought out in detail. 
Mr. Kiimmel gives prominence to the hypothesis of the extraordi- 
nary sinking of the floor of the Mexican Gulf, etc., thereby accounting 
for the greater portion of the subsidence of the valleys. It is gratify- 
ing that the reviewer accepts the evidence of the changes of level to 
the same proportion as the author, although suggesting a somewhat 
different character. The question of determining the amount of local 
deformation of the continent as different from the general movement 
is doubtless one of the difficult points; but the author allowed any 
amount up to 4000 feet for covering the abyssmal subsidence in excess. 
of the general movement south of the Mississippi. Whether too much 
or too little cannot yet be said. But amongst the Bahamas there is a 
better yard-stick. The drowned valleys reach to a depth of 12,000 or 
14,000 feet, amongst islands, banks, and in the edges of the continental 
plateau, which last is submerged to no more than 4ooo feet. Thus we 
cannot deduct for exaggerated marginal depression more than this 
amount in some places, and in others not even so much. However, 
the writer hopes to remove a few of the obscurities in the continental 
history, and thanks the reviewer for pointing out some of the greatest 
needs in elucidating the investigations of the great changes of level of 
land and sea, much new data being already at hand. 
J. W. SPENCER. 
Ueber Archaeische Ergussgesteine aus Smaland. Von Orto 
NORDENSKJOLD. (Bull. of. the Geol. Instit. of Upsala, Vol. L.,. 
NO: 2/1803, PP. 125.) 
Of all rock names probably the most indefinite, and at times the 
most convenient, are the names: greenstone in America, petrosilex in 
France, fe/stfe in England, and Aaleflinta in Sweden. Many, and. 
