Abstract: An improved marsh case is disclosed. The marsh case contains and protects a geophone, which is inserted into the earth in the course of oil exploration. The marsh case provides an cap having an upper opening through which wires pass to the geophone and a lower internally threaded opening that attaches to the body of the case. The body of the case provides an upper externally threaded opening which attaches to the cap, and a lower internally threaded conical surface which allows a threaded cylindrical surface of a spike to be attached. The threads of the body are slightly tapered, thereby relieving some of the stress that would otherwise be applied to the threads. The rim of the upper external threaded opening of the body and an internal annular shoulder in the cap compress an O-ring, thereby making a water-tight seal.