Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
Blackboard Inc. United States Court of Appeals for the Federal Circuit. A ruling was made by the Court of Appeals on July 27, 2009 that the 38 patent claims made by Blackboard in its suit against Desire2Learn were invalid. The dispute was resolved, when Blackboard and Desire2Learn announced on December 15, 2009 that each company was settling all ongoing litigation between them and had made a cross-licensing agreement. In April 2010, the firm abandoned patent 6,988,138, and in November that year the company's legal counsel announced the patent's "official termination" and stated that Blackboard had ended its appeals. Blackboard Inc. Blackboard Inc.