1866. | Teneriffe. 14 
some hundred feet wide and thirty to forty deep, fell over this 
spring and cross without doing the least damage, which the peasantry 
attribute to the merits of the cross, forgetting that the water in 
falling over the precipice would form a curve, and thus could not 
touch the vertical wall below. 
From the great depth of this ravine, the various rocks that form 
its perpendicular sides can be observed, as they form a perfect 
section; the uppermost rock consists of decomposed phonolite, 
below rough trachytic lava, with vegetable mould to the depth of 
three feet ; next is a sort of volcanic breccia or conglomerate, held 
together by a brown mud, and afterwards, beds of yellow and grey 
tuta four to five feet in thickness, succeeded by various alternate 
layers of dark trachy-dolerite and brown mud. As it was impos- 
sible to examine this interesting ravine on my journey up the Peak, 
I afterwards occupied myself several days in making a plan of it, 
and taking specimens of all the various rocks along a distance of 
several miles. 
The hygrometric state of the atmosphere showed that we were 
approaching the lower region of the clouds, the temperature fell 
rapidly, and the wet-bulb thermometer showed absolute saturation, 
at the same time vegetation became so luxuriant, that it was 
difficult to observe the nature of the lavas. 
The tree-heaths were of considerable size, some were 18 feet high, 
with stems nearly 30 inches in circumference; they were mixed 
with laurels, cystus, and various other arborescent shrubs. It is 
worthy of remark, that the leaves were of a uniformly dark-green 
colour. The luxuriant vegetation of this zone is no doubt owing to 
its greater humidity, as the clouds generally remain at this eleva- 
tion during the night and the early part of the morning. As we 
advance to the upper verge of this zone, the air contains less 
moisture, the radiation becomes much greater, and the vegetation 
less luxuriant, with the leaves of a light-green instead of a dark- 
green colour. 
The lavas appeared to have flowed in numerous streams from 
different openings, and their appearance varied considerably accord- 
ing to the angle they flowed over; for instance, where it had run 
up a slight ascent, it was twisted and contorted, as if it had been 
less viscous, showing that the surface had become refrigerated. I 
took specimens of some of the lower streams which were of trachyte, 
containing pyroxene, hornblende, and mica; over them were other 
streams, of what may be termed a dolerite lava, it contained ery- 
stals of red, brown, and greenish colours, apparently labradorite, and 
oxene: some of the other streams contained crystals found in 
both kinds of lava, coupled with hornblende and olivine (peridote) ; 
they may be fairly called, I think, a sort of trachy-dolerite ; they 
were all highly magnetic. Many of the lavas were much decom- 
