60 TRANSACTIONS OF THE [Nov. 14, 
talban system’, and indeed the description of the typical Montal- 
ban series? would make a very good description of the island. 
Macfarlane’ likewise pronounces them Montalban. But the ob- 
jection is made by the other side that similarity of rock structure 
does not imply identity of age, and that the question must 
be decided by stratigraphical considerations. Working on this 
line, Prof. Dana has sought to establish the connection between 
these schists and the fossiliferous Lower Silurian beds further 
north, and to show that they have simply been carried further in 
the process of metamorphism.‘ ‘The crucial test of the conclu- 
sion is the connection between the two at Fishkill, which is be- 
yond the limits of this paper. 
Prof. Stevens® pronounces them Taconic, and makes a separate 
group, the ‘‘ Manhattan Group,” for their accommodation. 
But they differ in no important particular from the mainland 
and do not deserve the distinction. 
The question narrows therefore to the problem of local con- 
figuration. ‘lhe sections on the map show the character of the 
bedding.’ The prevailing strike of the rocks is, by the compass, 
N. 40 E., and the dip varies from great contortions along the 
line of Third and Fourth avenues, to a general angle of 45° W. 
in the eastern part, and to verticality in the western. Sections 
L. M. and J. K. have been partly taken from Dana,’ but some 
attempt is made to indicate surface configuration, which his sec- 
tions do not show. It is interesting to note how the fold, which 
is shown in the limestone at 138th street, is continued in the 
contortions to the south, shown in section G. H., and doubt- 
less might with truth be exhibited in the other sections, but it 
was not possible to get local observations, owing to buildings. It 
is very possible that it would be true to map other folds. _ Prof. 
Stevens gives a section in the Lyceum Annals, Vol. VIII., p. 
108 seq., in which four or five synclinals are suggested and a bed 
-of limestone assumed under the Hudson. But this did not seem 
to me to be warranted by the facts. If the original stratum has 
been doubled up so many times, it could only have been very thin 
when horizontal. Now much of its upturned edges must have 
been eroded, and if we supply but very little and imagine the 
folds flattened out, the bed would cover a good deal of horizontal 
territory. But it does not seem reasonable that so broadly ex- 
1 Chem. and Geol. Essays, p. 248. 
2 Tdem, p. 244. 
3Geol. Trav. Handbook, p. 68 and note. 
4 Limest. Belts of West’r Co, Am. J. Sc., XX., 21 and following 
numbers, especially pp. 371 and 455. 
5 Annals Lyc. Nat. Hist., Vol. VIII., p. 108 seq. 
6 A large chart giving a detailed description of dips and strikes is de- 
posited in the Library of the Academy. [Ed.] 
7Am., Jour. Sci., XX., pp. 486 and 441. 
