on pH. Additional readings were secured occasionally from pools 1a, b, and c on the headland and pool 4a on Crab Island. (1) Temperature Diverse factors affect the temperature of tide pools and fluctuations occur according to the conditions prevailing at the time of determination. A high-level pool, which has been exposed for a long time may show a considerable rise in temperature on a fine sunny day, though the extent of the rise will depend very largely upon the size and depth of the pool. A shallow pool at low levels, although exposed for a relatively short time, may attain quite high temperatures during the summer months. At Narrow Neck is was found that topography of the rocks and aspect of the pool influence the temperatures to a considerable extent, and may even mask the effect of level. Fluctuations in air temperature may also be reflected in the temperature of a pool. This is demonstrated by readings for pools 1–3 on May 30 (Fig. 7) and for pools 4 and 4a in January (Fig. 8), though it will be noted that, in general, air temperature is below that of the pools. Fig. 7—Hourly changes in pool temperatures for May 30 (A), June 30 (B), July 31 (C). Air temperature changes are shown on May 30. The temperature reached by a pool on any given day depends very largely on the time of low water. If low tide occurs in the middle of the morning, the temperature will not reach a high value before the pool is flooded once more. If low tide occurs at mid-day or early afternoon a much higher value will be reached before the pool is reflooded. (a) Daily change. The daily change in temperature depends mainly on local conditions. Those pools which remain in the sun during the period they are exposed show a steady increase in temperature, whereas those which become shaded soon show a decrease. This fact is illustrated in the graphs for pools 1, 2, and 3 (Fig. 7). These high-level pools are on the south side of the headland and thus receive the sun's rays only up till mid-day or earlier, depending on the season of the year.