As you report, Peter Kelemen and Juerg Matter, both from Columbia University in New York, have suggested that carbon dioxide could be pumped from places where it is produced into underground strata of peridotite, a type of rock with a voracious appetite for the troublesome gas (“Eating Carbon,” November 15, 2008). One of the main rocks in the upper mantle, it occurs some twenty kilometers below the surface. Some researchers have looked into the possibility of grinding peridotite and using it to soak emissions from power stations, but the process is too expensive, partly because of high transportation costs. Now, you also report that this rock occurs on the surface, as well. In particular, it occurs in the Omani desert, which Kelemen and Matter have studied extensively, some Pacific islands, along the coasts of Greece and Croatia, and in smaller deposits in America. Concerning Greece and Croatia, here is a welcome opportunity for the European Union. Provided, of course, the producers of carbon dioxide, such as power stations, located along these countries’ coasts do not interfere with tourism there.