The right-hand stamp is a cross section of the outer part of the earth showing the formation of volcanic islands along a line where one lithosphere plate (crust and upper mantle 50-100 miles think) collides with and rides over another such plate, pushing the latter down into the more plastic asthenosphere.
(a cross section of the outer part of the earth; showing; the formation of volcanic islands along a line)
a cross section of the outer part of the earth
showing
the formation of volcanic islands along a line