Another source quotes 15–25% clay and the remainder sand and coarser particles up to cobbles , with no deleterious effect.
ɐnˈʌðɚ sˈoːɹs kwˈoʊts fˈɪftiːn twˈɛnti fˈaɪv pɚsˈɛnt klˈeɪ ænd ðə ɹᵻmˈeɪndɚ sˈænd ænd kˈoːɹsɚ pˈɑːɹɾɪkəlz ˌʌp tə kˈɑːbəlz , wɪð nˈoʊ dᵻlɪtˈɪɹiəs ɪfˈɛkt.