390 The American Geologist. December, isue 
from lower altitudes, at which Cretaceous and early Tertiary baselev-' 
elling of this peneplain took place, is referred to some staj^e in the mid- 
dle or later jjart of the Tertiary era, previous to the Lafayette period. 
Since that differential uplift, which gave the present long and gradual 
slopes of the upland areas, the rivers have channelled their meandering 
valleys, which vary in size up to a width of several miles and in depth 
from 100 to 500 feet. Much additional examination of the river courses 
is needed, however, to explain many of their minor features and their 
detailed history. w. u. 
On tJie Existence of Pre-Caiahrian and Post Ordovk- inn Trap Dikea 
in the Adironilacks. By H. P. Cushincj. (Trans. N. Y. Acad. Sci., 
vol. 15, pp. 248-252, Sept., 189G.) From recent work in New York state, 
chiefly in Clinton county. Prof, dishing has become convinced that 
there were two periods of intrusion of dike rocks in the Adirondack re- 
gion, instead of one period as formerly thought. This is an interesting 
I point in the history of the Adirondacks and in the study of these dikes, 
for our knowledge of which we are chiefly indebted to Profs. Kemp and 
Marsters. Prof. Cushing presents in brief the evidence for the separa- 
tion of these dikes into two series, and concludes that one series fol- 
lowed the dynamic metamorphism of the gneiss, limestone and gabbro 
series of the Adirondacks, but antedated the Potsdam sandstone. The 
typical rocks of these dikes are diabases. The second series cuts all the 
strata up to and including the Utica shale, and the dike rocks are 
"trachyte " (bostonitej and basic rocks, mostly camptonites and monchi- 
quites. u. s. g. 
Structural Detail s ill the Oreen Mountain Region and in Eastern 
Neiv York. By T. Nelson Dale. (U. S. Geol. Survey, 16th Ann. 
Rept., pt. I, pp. 54.3-570, 1896.) The author has collected in this paper 
excellent illustraticms aad brief descriptions of various structural de- 
tails which he has observed in his work in the Green mountains. The 
phenomena illustrated are folds of several varieties, false bedding, ob- 
scuration of bedding by cleavage, cleavage, cleavage banding, stretch- 
ing, etc. These illustrations from the note book of a geologist working 
in a crumpled and metamorphic area are of much interest, and show on 
a small scale many important details of structure, details which the 
worker in such an area must be continually searching for. u. s. g. 
A Handbook of Rocks, for use tvithout the microscope. J. F. Kemp. 
Printed for the author. New York, 1896, roy. oct. 176 pp. This is a 
general elementary treatise on rocks, the design being to furnish a com- 
pendium for teachers, based mainly on American rocks and literature. 
Its author has traversed essentially an untrodden field, in bringing 
American petrography together into a systematized form, and grouping 
the facts in a reasonable scheme of modern classification. He has thus 
rendered American geology a great service. In doing this he has left 
signs of his route all along his course, and anyone can follow and 
amplify his work. These signs are the constant references to American 
literature which are massed in connection with the chemical analyses 
