Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of construction materials maker Vulcan Materials (NYSE: VMC) erupted today, jumping as much as 34.1% amid crushingly heavy trading.

So what: Rival Martin Marietta Materials (NYSE: MLM) just posted a $4.7 billion hostile takeover offer for Vulcan. The companies discussed a merger last year, but nothing came of it, so now we have the smaller company running the show with a stock-swap bid for the larger one.

Now what: Martin Marietta's shares also gained nearly 5% today as investors saw value in the proposed deal. Since it's a stock-for-stock transaction, Vulcan's market cap is now larger than the bid would indicate. Combining these all-American materials specialists would unlock economies of scale. Vulcan investors who were disappointed by the recent dividend cut should welcome this offer with open arms.

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Fool contributor Anders Bylund holds no position in any of the companies mentioned. Motley Fool newsletter services have recommended buying shares of Vulcan Materials. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinion, but we all believe that considering a diverse range of insights makes us better investors. Check out Anders' holdings and bio, or follow him on Twitter and Google+. We have a disclosure policy.