REVIEWS 653 
upwards of twenty-five large volumes, all of which are devoted, wholly 
or in part, to the geology of the Ozarks. 
Growing out of this official work, either directly or indirectly, there 
-have appeared from time to time other contributions to a geological 
knowledge of the region. The Arkansas geologists have been espe- 
cially active in setting forth information of the greatest value concern- 
ing the ferra incognita of only ten years ago. Branner, Winslow, Pen- 
rose, Hopkins, J. F. and H. S. Williams, and Griswold have all given 
us geological accounts of great interest. The results of their work 
have been most acceptable. An outgrowth of this same work has been 
to induce others to take up attractive lines of investigation thus pointed 
out. At intervals there have been given short sketches that fill in 
important gaps. 
Isolated from all localities where similar rock successions were 
already carefully studied and were well known, the workers in Arkansas 
were obliged to set up a geological rock classification of their own. 
The sequence of terranes could be correlated with those of well-known 
regions only in the most general way. Much has been done of late to 
clear up the existing uncertainty of stratigraphic equivalency. The 
early Paleozoic rocks still resist all attempts of detailed classification 
and ‘correlation. The Carboniferous has yielded more gracefully. 
With the latest contribution, by Drake, the last link binding the strati- 
graphy of the southern region to the northern has been forged. 
The “ Thickness of the Paleozoic Sediments in Arkansas,” by Pro- 
fessor Branner, may be taken as a concise summary of the results of 
the Arkansas geological survey regarding the sequence and develop- 
ment of the older rocks of the southern Ozarks. The article is accom- 
panied by a small but excellent general geological map of the state, and 
gives a classification of the formations recognized, and their observed 
thicknesses. The enormous estimated thickness of the Coal Measures 
is especially noteworthy. These figures come somewhat in the nature 
of a surprise, manifestly to the author also, for he takes particular pains 
to present clearly the detailed evidence upon which he has reached his 
conclusions. He says: “There is, of course, nothing remarkable 
about the thickness of any of the Arkansas sediments except in the 
case of the Lower Coal Measures. So far as I can learn the thickness 
of the Carboniferous rocks in this section is greater than that of the 
sediments of the same age in other parts of the country or of the 
world.” 
