Also many shrimp-like animals (Alima) the bodies of which were divided distinctly into an interior and posterior portion; all the shrimp-like animals which we have caught whose bodies are thus divided swim by doubling up the posterior part close to the anterior, and then giving a stroke with great rapidity outwards.  These little animals are very susceptible, and when they have been in the least injured their limbs remain in so constant a state of tremor that the motion communicated by them resembles that which would be caused by the passage of a rapid succession of electric shocks, rather than any other I am acquainted with.

GEOLOGICAL OBSERVATIONS AT ST. HELENA.

July 21.

After visiting Longwood and Napoleon’s tomb we rode to Flagstaff Hill to search for fossil shells.  The whole soil that I saw was composed of decomposed old volcanic rocks; but I saw no rock but basalt in different stages of decomposition; sometimes it assumed the form of porphyry.  I also saw veins of quartz, gypsum, and jasper.  On a part of Flagstaff Hill there was a thin stratum of calcareous earth, in which shells are found.  My hip was so painful that I could not climb to the point where these were, but an artillery soldier ascended and brought down some, and of these I had several specimens given me; they are found associated with bones which are apparently those of birds.  None of these bones were given to me but I saw and examined several specimens.  The shells are very numerous at this point.

On returning into town I found several specimens of dead land shells, apparently recent; these lay on the sides of the hills, partly buried in the soil, and bore the appearance of having been washed into this position by the heavy rains.

July 22.

Rode over in the morning to Longwood, and then proceeded to Gregory’s Valley, lying between Longwood and The Barn.  This valley, nearly 1700 feet in depth, appears at one period to have been the scene of great volcanic disturbances.  The lowest rock I saw was a compact porphyritic one.  The upper strata of basalt were in a state of rapid decomposition; but the whole of the valley was traversed by basaltic dykes in every direction; these crossed one another in such a way that it was easy to tell their relative ages; for instance several of them were in the form of: 

So that one had been forced from its position by another long subsequently to its formation.

The general form of Gregory’s Valley is a large basin bounded by a lofty precipitous mountain on one side called The Barn, and having a very narrow opening seaward, through which a small stream has cut its way.  A remarkable circumstance connected with the basaltic dykes is that they are composed of a more compact basaltic rock than the basalt which they penetrate, so that whilst the rock has mouldered away these basaltic dykes have remained standing; and, as in the progress of their decay they split up, they present the appearances of walls built by human hands, with regular layers of stones, and which traverse the ravines of the island in all directions.