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. Blackboard acquired Sequoia Retail Systems in May 2016. Though previously a public company, following its 2011 buyout by Providence Equity Partners Blackboard now operates as a private company. The company's headquarters are in Washington, D.C. and it has offices in Asia, Australia, Europe and in several locations in North America. The initial product to be offered by the company was its course management software, first available in 1998. The latest version, Blackboard Learn 9.1, was released in April 2010. This is a learning management system that provides a learning system for course delivery and management for institutions; a community and