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The deep scattering layer (DSL) in the Gulf of Mexico has been studied, over a period of three years, utilizing a precision depth recorder operating at 12 kHz. The DSL appears to be divided into four main daytime layers. The west-central Gulf shows little deep layering. No definite correlation of DSL and physical parameters was arrived at. The DSL was not found to be seasonally variable. There were some indications that the DSL shoals to the north. Maximum rates of evening ascent of 3.4 fm/min (6.2 m/min) and morning descent of 5.9 fm/min (10.8 m/min) were determined. The length of time for ascent (2 hr) and descent 3 1/2 hr) are arrived at. Examples of evening ascent, morning descent and the dawn rise are presented. Response of the DSL to a total solar eclipse and cloud cover are discussed. (Author)