The formation is gneiss, interstratified with quartz, and traversed by veins of felspar; and the rock is generally decayed to a considerable depth on the plateau, and disintegrated so as to form a gritty clay. In the eastern part the soil is a light reddish loam; but on the western and loftier half it is very poor, being a heavy black peat several feet thick, with a stiff and plastic yellowish clay as a sub-soil. The rains on the Neilgherry hills have the effect of mixing the decaying grass with the decomposed rock, and a rich soil is thus formed; but on the plateau of the Pulneys this operation does not appear to take place, the one becoming a black peat, and the other a stiff clayey subsoil. These remarks, however, only apply to the interior valleys, for on the outer slopes, overlooking the plains of Madura, there is plenty of good soil, and magnificent forests clothe the mountains at the foot of the perpendicular walls of gneiss which form the southern ridge of the Pulneys. The climate of the Pulneys, as regards temperature, very closely resembles that of the Neilgherries. At the time of my visit, in the end of November and beginning of December, the season was very late, though there were thick mists and showers of rain every afternoon. This is the time of the north-east monsoon, and the streams swell to torrents after every shower. During the first two months in the year it is very cold, and the ground is often covered with frost on the upper plateau. In March there are light showers of rain, which increase during April and May, and continue, with strong westerly winds, until October. Thus the Pulneys are within the influence of the south-west monsoon.[435] In June and July, the warmest months, the thermometer never falls below 50°, nor rises above 75°; and the westerly winds, with occasional rain, continue during August and September.