Thermogravimetric studies on the St. Jean Vianney clay from Quebec, Canada, have indicated four major thermal events. These events are best presented by means of the Derivative Thermogravimetric (DTG) curve which, until now, has been presented primarily as a histogram DTG plot. However, the tangent DTG plot gives greater distinction between thermal events and locates nine thermal events; the original four as well as five sub-events. A comparison of two quickclays, the St. Jean Vianney clay and a Norwegian clay, using the tangent DTG plot shows the complex mineralogical nature of the Canadian quickclay, while the Norwegian clay appears to have a relatively simple mineralogy.