Abstract
The author studied the volcanic rocks of the coal field around Nagasaki City, for the purpose of considering the possibility of igneous intrusion into the coal seams of undeveloped area within the submarine coal field west of Nishisonoki Peninsula.
The volcanic rocks in this area may be classified into the following three groups.
a Neogene dacitic-andesitic lava flows and pyroclastic rocks.
b Basaltic rocks of the pigeonitic rock series.
c Andesite or andesitic basalt of the hypersthene rock series.
The group "a" is distributed around Nagasaki City, and both the group "b" and "c" develop along the western coast of Nishisonoki Peninsula, or in the islands or in the sea bottom west of the peninsula, where the extrusion of "b" may have probably preceded that of "c". The intruding volcanic rock of Nagayo near Nagasaki is similar in petrological characters to those of group "a". The igneous rock intruding coal seams of Hajima colliery belongs to group "b". These suggest the possibility of igneous intrusion into coal seams where the surface volcanic rocks may be present near by. Thus, it cannot be denied that there may be some igneous intrusions of "b" or "c" type into coal seams in the undeveloped area between Matsushima and Iojima.
