May prove LaSalle explored Mississippi before Marquette QUINCY - What's certain is that something's written in the stone. What's less certain is whether the markings have any historical significance. Now, University of Illinois scientists have agreed to examine the limestone slab some believe proves French explorer Robert Cavelier de LaSalle was the first white man to see the upper Mississippi River in 1671 -- two years before Father Jacques Marquette and Louis Joliet made their famous trek. The foot high, 8-inch wide stone, which was found by a farmer in the early 1900s in Ellington Township north of Quincy, has...