1895. ] NEW YORK ACADEMY OF SCIENCES. 29 
time of disturbance and metamorphism of these rocks. In thin 
section they show no sign of having suffered from the dynamic 
action which has so profoundly affected the other rocks and 
whose effect is so beautifully shown in sections of the diorites 
by the bent and broken crystals, undulatory extinction and 
production of secondary minerals there exhibited. 
While in the main to be classed as diabsses, these dikes shade 
into andesite-like rocks through loss of the ophitic structure 
and development of a glassy groundmass. Specimens of more 
acid rock, rhyolites and micro-pegmatites, are not infrequent on 
the moraines, but only one such dike has been found in place, 
and no evidence is at hand as to their relation in time to the 
basic dikes. These dike rocks much resemble others of known 
Tertiary age occurring further to the south.* 
CoMPARISON WitH OTHER ALASKAN SECTIONS. 
The Coast range belt, of which the region under considera- 
tion is structurally a portion, is shut away from the Pacific. 
north of Cross sound, by the lofty peaks of the Fairweather 
range. If,as seems probable, this latter belongs structurally with 
the St. Elias range, it is of a much more recent date. 7?) Mite 
Glacier bay section presents many points of similarity with 
sections described by Dawson and Hayes from British Columbia 
and southern Alaska, so that a rough correlation may be at- 
tempted. A marked feature here is a limestone of great thick- 
ness, which, at least in part, is of Carboniferous age. Dawson 
describes such a limestone from the Dease river holding Fusu- 
lina,f and another from his section along the Stikine which he 
believes the same, though finding no fossils. Apparently the 
same limestone is mentioned by Hayes as occurring in the Taku 
valley.|| Furthermore Hayes reports black slaty shales appar- 
ently underlying the limestone, and Dawson describes from the 
Stikine a series of‘ hard argillites and grauwacke-quartzites, 
interbedded with shaly gray and brownish impure limestones,” 
which were “ not observed to hold staurolite, mica, or otherwise 
crystalline minerals like those of Wrangell, and otherwise differ 
somewhat in appearance from those.’’*| These rocks are below 
*For brief petrographic descriptions of specimens from these dikes : see G. H. 
Williams, Nat. Geog. Mag., Vol. IV., pp. 68-74. 
+See. H. F. Reid, Nat. Geog. Mae. Vol. IV, p. 24,and G. F. Dawson, Geol. Sury. Can. 
An. Rep. 1887-8, p. 12 B. 
1G. F. Dawson, Geol. Sury. Can. An. Rep. 1887-8, p. 33 B. 
7G. F. Dawson, Geog. Sury. Can. An. Rep. 1887-8, p. 55. 
| C. W. Hayes, Nat. Geog. Mag., Vol. IV., p. 138. 
§ Geol. Sury. Can. An. Rep. 1887-8, p. 55 B. 
