def plot_ts(fignum, dates, ts):
    """
    plot the geomagnetic polarity time scale

    Parameters
    __________
    fignum : matplotlib figure number
    dates : bounding dates for plot
    ts : time scale ck95, gts04, or gts12
    """
    vertical_plot_init(fignum, 10, 3)
    TS, Chrons = pmag.get_ts(ts)
    p = 1
    X, Y = [], []
    for d in TS:
        if d <= dates[1]:
            if d >= dates[0]:
                if len(X) == 0:
                    ind = TS.index(d)
                    X.append(TS[ind - 1])
                    Y.append(p % 2)
                X.append(d)
                Y.append(p % 2)
                p += 1
                X.append(d)
                Y.append(p % 2)
        else:
            X.append(dates[1])
            Y.append(p % 2)
            plt.plot(X, Y, 'k')
            plot_vs(fignum, dates, 'w', '-')
            plot_hs(fignum, [1.1, -.1], 'w', '-')
            plt.xlabel("Age (Ma): " + ts)
            isign = -1
            for c in Chrons:
                off = -.1
                isign = -1 * isign
                if isign > 0:
                    off = 1.05
                if c[1] >= X[0] and c[1] < X[-1]:
                    plt.text(c[1] - .2, off, c[0])
            return
plot the geomagnetic polarity time scale

    Parameters
    __________
    fignum : matplotlib figure number
    dates : bounding dates for plot
    ts : time scale ck95, gts04, or gts12