Lomnitz received his doctorate from Caltech in 1955 with a dissertation on creep measurements in igneous rocks. Its principal thesis, a logarithmic creep behavior observed in rocks, was reformulated as the "Lomnitz Law" by Harold Jeffreys in 1958. The Lomnitz law is expressed as, ε ε ( t ) = σ σ E 0 [ 1 + q ln ⁡ ⁡ ( 1 + a t ) ] , t ≥ ≥ 0 , where, ε ε ( t ) is the time-varying creep (or, strain), σ σ is the constant stress load on the material, E 0 is the shear modulus, a is a positive material constant, and q is the creep constant. Though the Lomnitz law was inferred empirically from rheological measurements on rocks, its validity was firmly established by Pandey and Holm by deriving it from the physical principles in the framework of fractional calculus. They had used a time-varying Maxwell model in their analysis and found that the underlying physical mechanism in rocks that led to the Lomnitz law was a linearly time-varying viscosity, η η ( t ) , η η ( t ) = η η 0 + θ θ t , where η η 0 is the constant part of the viscosity and θ θ t is the time-varying part of the viscosity, such that θ θ = d η η ( t ) / d t > 0 . Such a property with increasing viscosity with time corresponds to rheopecty, or anti- thixotropy, a special class of Non-Newtonian fluid. Pandey and Holm extracted the physical interpretation of the parameters of the Lomnitz law as follows: q = E 0 θ θ and a = 1 τ τ = θ θ η η 0 where, τ τ is the relaxation time during which the transition from the elastic- to creep-type deformation occurs. The mechanism underlying the Lomnitz law is that the time-varying part increases linearly with time and dominates over the constant part, θ θ t ≫ ≫ η η 0 . Further, since q ≪ ≪ 1 , for igneous rocks this implies the time-varying part of the viscosity dominates over the elasticity of the rocks, i.e., θ θ ≫ ≫ E 0 . Interestingly, the relaxation modulus of the time-varying Maxwell model was identified as the Nutting law from rheology. This physical justification has been lacking in both Nutting’s law and Lomnitz’s law since their inception in 1921 and 1956 respectively. As a result of these findings a useful physical interpretation of the fractional dashpot and hence the fractional derivatives was obtained.