The field dependence of magnetic remanence in laboratory deposited sediments is re-examined in terms of the average orientation of small grains of magnetite subject to the combined effect of an aligning field and thermal agitation. The classical (Langevin) formula for paramagnetic susceptibility is generalized to describe an assembly of grains with magnetic moments having a uniform distribution of values between zero and an upper limit, yielding a simple analytical expression in excellent accord with the pioneering measurements of Johnson, Murphy and Torreson. Comparison of theory and observation shows that the grain moments are intermediate between the values expected for single domains and multidomains, confirming the existence of pseudo-single domain effects, as deduced from observations of thermoremanence.