Polymer chains attached by one end to an impenetrable surface at high coverage exemplify a tethered layer of mesoscopic dimensions. At equilibrium, thermal fluctuations of the segment density profile of the brushlike layer reflect the tethered chain dynamics; the probing of these fluctuations by evanescent-wave dynamic light scattering is reported. By utilizing a set of terminally attached layers with thicknesses (L(0)) from 45 to 130 nanometers, it was found that there is a preferred wavelength of order L(0) of these fluctuations with a concurrent slowing down of their thermal decay rate. This technique could open the route for the investigation of the largely unexplored area of polymer surface dynamics.