52 
The American Geologist. 
January, 1896 
part of the state, belong to the Upper Carboniferous (Missouri stage) 
and Cretaceous. The beds of the latter are arenaceous in character 
and were named by White the Nishnabotna sandstone. 
A noticeable feature of the volume is its excellent geological maps of 
the counties reported upon. The maps are all drawn on a scale of one 
half inch to the mile. The color scheme adopted by the International 
Congress of Geologists has been followed in general. Minor subdi¬ 
visions of a formation are shown by pattern lines and where these divi¬ 
sions cannot be separated a solid color representing the major divi¬ 
sion is used. a. g. l. 
Fossil sponges of the Flint Nodules in the Lower Cretaceous of 
Texas. By J. A. Merrill. (Bulletin of the Museum of Comparative 
Zoology at Harvard college, vol. xxvn, [Geological series vol. hi], no. 
1, pp. 1-26, 1 pi.. July, 1895.) This paper is the first dealing with the 
microscopic structure of the Cretaceous flints of America, for the in¬ 
vestigation of flints has hitherto been chiefly confined to those of Eng¬ 
land, and has been carried on by English geologists. The specimens 
described by Prof. Merrill are nodules from a single locality near 
Austin, Texas, in the Caprina chalk of the Comanche series. The 
writer has regarded as proven that flint nodules have their origin in 
organic silica, and from this starting point directs his researches in 
three chief directions : 
1. The identification of the fossils (chiefly sponge spicules) found in 
the flints. 
2. The conditions of preservation of the spicules, and changes in 
them subsequent to deposition,—such as solution, crystallization, or 
replacement. 
3. The method of formation of the nodules. 
In the summary he draws conclusions as to the general conditions 
under which the flint bearing horizon of the Cretaceous was deposited. 
Among the fossils, Foraminifera. and sponges were found most abun¬ 
dantly. The Foraminifera belong chiefly to the Globigerina family, al¬ 
though Textularia were found in most of the sections examined. The 
sponge remains are mainly spicules, and it is noted as novel that the 
minute dermal spicules are better preserved and more numerous than 
the zonal varieties. Besides these easily identified fossils, fragments 
of what were suspected to be the shells of mollusks, and yellow plates 
of amorphous silica having the appearance of fish scales, were found. 
In the preservation and alteration of the spicules, the writer finds a 
decided difference between the globo-stellate and other spicules of the 
dermal layer on the one hand, and the zonal spicules on the other. The 
latter are seldom found perfect in form or outline. In almost every 
case a process of crystallization has been and is still at work, changing 
the original organic silica to mineral silica, like that which forms the 
main body of the flint where no organisms can be distinguished. This 
crystallization takes place in two distinct zones, penetrating inward 
from the outer surface of the spicule, and outward from the axial canal. 
