Soil classification based on CPT data is commonly carried out using classification charts which link the type of soil behaviour to the measured tip resistance, sleeve friction and pore water pressure. These charts have been successful in interpreting soil behaviour in young, saturated, uncemented soil deposits but often diverge from observations in samples in older deposits. The geotechnical investigation conducted for the 1915 Çanakkale bridge included 20 offshore boreholes with 18 adjacent CPT soundings conducted downhole that penetrated several meters into Miocene-age sediments. This paper investigates those data sets and proposes a modified chart for the classification of the Miocene deposits accounting for their microstructure. The proposed modification is useful for classifying Miocene deposits in similar geological settings through the performance of CPTs.