(Updates prices and adds analyst's comment, details)
* TSX down 40.16 points, or 0.27 percent, to 15,002.99
* Eight of the TSX's 10 main groups lower
By Solarina Ho
TORONTO, May 13 (Reuters) - Canada's main stock index fell for a third straight session on Wednesday, reversing early gains, as U.S. economic data disappointed the market, while rising gold miners limited the loss.
Canadian National Railway Co was the index's biggest heavyweight decliner. The country's biggest railway fell 2.04 percent to C$74.97. Canadian Pacific Railway Ltd was not far behind, falling 2.1 percent to C$214.94. The railways are in the index's industrials group, which retreated 0.9 percent.
Energy stocks reversed course and fell 0.3 percent after initially climbing on stronger oil prices. In the group, Encana Corp fell 3.9 percent to C$16.02.
"You're getting the offsetting effects of crude oil price up a little bit, which is good for energy stocks, but U.S. retail sales disappointed, which is still continuing to raise questions about the health of the U.S. economy," said Colin Cieszynski, senior market analyst at CMC Markets Canada, noting the United States is Canada's largest export market.
"Overall, stock markets are struggling here. The U.S. markets are kind of going sideways, and it looks to me Canada's doing about the same."
At 10:26 a.m. EDT (1426 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 40.16 points, or 0.27 percent, at 15,002.99.
All but the materials and utilities groups gave back early gains. The index's financial sector, home to banks and insurers, was down 0.5 percent, with Manulife Financial Corp falling 0.9 percent to C$22.82.
The most influential positive movers on the index included Goldcorp Inc, which led a number of gold miners into positive territory. Goldcorp rose 3.03 percent to C$23.43, while Barrick Gold Corp advanced 3.1 percent to C$15.89.
The overall materials group climbed 1.3 percent.
Gold miners were helped by higher gold prices, which rose on the back of a weaker greenback. Gold futures climbed 1.6 percent to $1,211.5.
U.S. retail sales missed forecasts in April, holding steady as households scaled back big-ticket purchases such as cars. Economists had forecast a 0.2 percent rise.
Declining issues outnumbered advancing ones on the TSX index by 124 to 119, for a 1.04-to-1 ratio on the downside.
$1=$1.20 Canadian Reporting by Solarina Ho; Editing by Peter Galloway