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

Quiet holiday trading continued Tuesday, with the path of least resistance proving to be up today. The S&P 500 and Dow Jones Industrials gained between a quarter and a half percent on the strength of positive economic news from the manufacturing and housing fronts. Among winning stocks, Twitter (NYSE:TWTR), Westmoreland Coal (NASDAQ:WLB), and Amyris (NASDAQ:AMRS) were close to the top of the list Tuesday.

Twitter jumped more than 8% Tuesday, adding to gains that have taken the social-media stock up 55% from its first-day IPO close less than two months ago. Some analysts attributed the move to a short squeeze for the social giant's shares, but the broader reason behind the move might simply be that Twitter is gaining more legitimacy as a major player not just in social media but in media generally. In particular, Disney's (NYSE:DIS) selection of Twitter Chairman Jack Dorsey to join Disney's board shows the value of social-media knowledge to Disney's overall mission. With stocks throughout the social-media world climbing, Twitter faces plenty of competition, but it also occupies a position of strength from which to stake its claim to the industry's potential long-term profits.

Westmoreland Coal climbed 11% after it agreed to buy seven Canadian thermal coal mines from Canada's Sherritt International for $435 million, as well as some other assets. With Sherritt divesting its coal operations to concentrate on other commodities, including oil and nickel, Westmoreland's move doubles down on the hope that a rebound for coal will come sooner rather than later. That's a risky move, but further consolidation in the industry could help put surviving players in better position to reap the benefits of the next cyclical upturn -- whenever it comes.

Amyris gained almost 7% after announcing that it had sold $28 million in convertible notes to existing and new investors in a private placement. The renewable chemicals and fuel company also said that major investor Total (NYSE:TOT) had agreed to cancel more than $6 million in already outstanding convertible notes in order to finance its share of the new deal. CEO John Melo pointed to the success of Amyris in meeting its funding milestones as an important step in the company's growth, but the key to long-term success for Amyris will come from its being able to find more markets for its renewable products.