Geology.'--The Eastern Cordillera., which, however, is but little known, appears to consist, as in Bolivia, chiefly of Palaeozoic rocks; the western ranges of the Andes are formed of Mesozoic beds, together with recent volcanic lavas and ashes; and the lower hills near the coast are composed of granite, syenite and other crystalline rocks, sometimes accompanied by limestones and sandstones, which are probably of Lower Cretaceous age, and often covered by marine Tertiary deposits.
Great masses of syenite and diorite were intruded during the Tertiary period, and within the curve of the folded belt a line of recent volcanic cones stretches from western Baluchistan into eastern Persia.
A syenite massif of this age occurs at Mittagong; and leucite has been discovered in Carboniferous basalts by David.
Planted blocks of syenite from Norway side by side with them.
The olive green syenite found on Mount Ascutney, near the Connecticut river, in Windsor county, is a hornblendeaugite.
Great masses of granite, syenite and diorite were intruded at this period, and send tongues even into the andesitic tuffs.
Large quantities of this syenite were used in building the Assuan dam (1898-1902).
At Assuan (Syene) the well-known syenite of Werner occurs.