A technique is described for the use of a probe-type ultrasonic device to disaggregate selected Triassic continental sandstones, siltstones, shales, and several other rock types. The samples used in developing this method were particularly resistant to disaggregation by standard methods, which failed or were minimally successful. The average time needed to disaggregate samples was much less for those treated with the probe sonifier than in the tank-type of sonifier. There are however similar problems which may result from the use of either of these, including the necessity of guarding against rounding of grains and loss of relatively softer minerals by abrasion. Sandstones average 25 minutes per sample as compared with 13 minutes for shales and 58 minutes for the siltstones. Limestones or marbles take considerably longer with very poor results unless they are calcarenites in which the fragments are well separated by clay minerals. The time referred to includes only the actual running time of the apparatus and not the time involved in other phases of the procedure The probe-type ultrasonic device may also be used satisfactorily at the beginning of hydrometer or pipette analysis of clays in lieu of overturning the graduate cylinder or stirring with other devices In addition, if flocculation occurs after the test has begun, the probe may be inserted directly into the graduate cylinder and run for 5 to 10 minutes. This eliminates the necessity of either transfer of the suspension for further stirring, or stirring with large stirring devices which might result in some loss of the suspension.