IX. Notes on the Geology of the Island of Yesso, Japan, 

 FKOM Observations made in 1862. Bv W. P. Blake. 



Read February 21, 1872. 



The sjilient features of the geology of the Island of Yesso, Japan, 

 are volcanic. Symmetrical cones, snow-capped for a great part of 

 the year, are the first landmarks that greet the eyes of the marine, 

 as he approaches the coast, and are tlie last to disappear as he leaves 

 it behind. The cone of Esaii, in a solfataric condition, forms the east- 

 ern and southern headland of the island, not far distant from the port 

 of Hakodadi and from Komangadaki Mountain, another solfataric 

 cone which rises conspicuously u})on the southern shore of Volcano 

 Bay, at about the same distance from Hakodadi. This last mentioned 

 mountain was in a state of violent eraption a few years ago, and threw 

 out an enormous quantity of ashes, pumice, and liot water. J'urther 

 north, beyond Volcano Bay, the beautiful cone of Shiribets is grouped 

 with several others, but all of them are remarkable for their symmetry 

 and grandeur. Most of these volcanic mountains may be regarded as 

 extinct, though many yield quantities of sulphur and emit steam. At 

 an early period their activity must have been prodigious, for almost 

 everywhere throughout the island, or at least the southern portion of 

 it, so far as explored, there is a vast deposit of fragments of trachyte, 

 lava, scoriae and volcanic debris. These materials are generally in 

 the form of a stratified lirecciated conglomerate, sometimes alternating 

 with finer materials, such as beds of sandstone and of volcanic ashes. 



A coarse conglomerate of this formation is found bordering the 

 island from Esau nearly to Komangadaki, and extensively upon the 

 western coast, as in the neighborhood of Iwanai. It is also found 

 extensively developed in the interior. 



Older and stratified formations ap})ear to form the basis or founda- 

 tion for the volcanic formations. At Ota, on the west coast, granitic 

 and metamorphic rocks, in well defined outcrops, form a rugged 

 coast. In tlie interior they form the principal watershed, and give 

 rise to many rivers, in the beds of which gold is found in deposits 

 which can be profitably worked. These metamor})hic strata are 

 uplifted, and generally trend northwest and southeast, and show 

 flexure and bending exactly as in other and better known regions- 

 Slates, sandstones, and limestones are found also at Esan, Shuokobi, and 



Trans. Connecticut A.cad., Vol. II. 22 Deokmber, 1872. 



