A dart and plug dropping head in combination with a well casing for use in sequentially dropping one or more plugs (176, 177) and darts (199, 202) into the well casing, comprising: a) a housing having an inlet at its upper end adapted to be fluidly connected in line with the lower end of a top drive, an outlet generally aligned with the inlet; b) a main flow channel that connects the inlet and the outlet; c) a plurality of valving members (43, 44, 45) spaced between the inlet and the outlet, each valving member (43, 44, 45) having a flow bore, and being movable between open and closed positions; d) one or more fluid flow channels that enable fluid to bypass the valving members (43, 44, 45) when a valving member (43, 44, 45) is in the closed position; e) at least one of the valving members (43, 44, 45) having a cross section that, in the closed position, does not allow fluid flow in the main flow channel; f) wherein fluid flow in the main channel flows around the valving member (43, 44, 45) when it is in the closed position and through the valving member (43, 44, 45) when it is in the open position; g) a sleeve above each valving member (43, 44, 45) that is configured to support a dart (199, 202) when the valving member (43, 44, 45) below the sleeve is closed; h) a plurality of darts (199, 202) in the housing, each dart (199, 202) above a valving member (43, 44, 45), wherein in the open position each valve flow bore permits a dart (199, 202) to pass therethrough, and circulating fluid to pass downwardly therethrough when a dart (199, 202) is not in the valve flow bore; i) a connector (174, 175) that connects the housing to the well casing; j) a pair of casing plugs (176, 177) that are contained in the well casing below the connector (174, 175), wherein each casing plug (176, 177) is receptive of and interlocks with a dart (199, 202) that is dropped from the housing; wherein the casing plugs (176, 177) are arranged one above the other in the well casing. a) a housing having an inlet at its upper end adapted to be fluidly connected in line with the lower end of a top drive, an outlet generally aligned with the inlet; b) a main flow channel that connects the inlet and the outlet; c) a plurality of valving members (43, 44, 45) spaced between the inlet and the outlet, each valving member (43, 44, 45) having a flow bore, and being movable between open and closed positions; d) one or more fluid flow channels that enable fluid to bypass the valving members (43, 44, 45) when a valving member (43, 44, 45) is in the closed position; e) at least one of the valving members (43, 44, 45) having a cross section that, in the closed position, does not allow fluid flow in the main flow channel; f) wherein fluid flow in the main channel flows around the valving member (43, 44, 45) when it is in the closed position and through the valving member (43, 44, 45) when it is in the open position; g) a sleeve above each valving member (43, 44, 45) that is configured to support a dart (199, 202) when the valving member (43, 44, 45) below the sleeve is closed; h) a plurality of darts (199, 202) in the housing, each dart (199, 202) above a valving member (43, 44, 45), wherein in the open position each valve flow bore permits a dart (199, 202) to pass therethrough, and circulating fluid to pass downwardly therethrough when a dart (199, 202) is not in the valve flow bore; i) a connector (174, 175) that connects the housing to the well casing; j) a pair of casing plugs (176, 177) that are contained in the well casing below the connector (174, 175), wherein each casing plug (176, 177) is receptive of and interlocks with a dart (199, 202) that is dropped from the housing; wherein the casing plugs (176, 177) are arranged one above the other in the well casing.