Here is a good article published in "appellationamerica.com".

http://wine.appellationamerica.com/wine-review/Randall-Grahm-on-Terroir.html

By the way...There is not an official definition of "Terroir" in English dictionaries (I looked in 6 dictionaries). In French, Terroir means:" Soil and climatologic specifications for an agricultural purpose".
In fact, this is the last official definition accepted by the French academy. However, since 1606 to nowadays, the definition was mainly focused on soil and was forgetting the "climate" factor.
As a reminder, this is a mistake to associate ONLY "terroir" with wines. For example, a truffle will taste totally differently from a growing zone to another.