SCIENTIFIC SUMMARY. 
89 
steam at a high temperature, which, being converted into water by contact, 
raises the temperature of the water, which in turn, as the store of heat is 
accumulated, rises by rents and fissures to the surface in the form of thermal 
springs. There seems no doubt that hot springs have a direct connexion 
with volcanoes. 1. Hot springs are present in all volcanic areas. 2. Where 
not connected directly with volcanoes, they are found situated, as in the 
Pyrenees, the Alps, and the Himalayas, upon lines of dislocation and dis- 
turbance, where volcanic force, if not visible at the surface, has been in 
operation far down beneath. 3. Hot springs distant from volcanic disturb- 
ances are nevertheless affected by them. Thus the 11 Source de la Peine,” 
at the baths of Luchon, in the Pyrenees, was raised suddenly during the 
great earthquake of Lisbon in 1755, from a tepid spring to 122° Fahr., a heat 
which it has since retained. Although springs, as a rule, carry carbonate of 
lime and sulphate of lime in solution, the hotter thermal springs alone con- 
tain large quantities of silica in solution. For example : the hot spring of 
St. Michael, in the Azores, having a basin 30 feet in diameter, is surrounded 
by layers of travertin many feet in thickness, composed of siliceous matter 
deposited on wood, reeds, ferns, &c. The hot springs of New Zealand are, 
perhaps, the finest, exceeding even the Great Geyser in Iceland, which also 
deposits enormous quantities of silica from its waters on cooling, originally 
held in solution. 
Injection of Crinoids by Silica. — A Silurian limestone which was recently 
examined by Dr. Dawson, was, says Dr. Sterry Hunt, F.R.S., found by him 
to consist almost wholly of comminuted organic remains, including fragments 
of trilobites, gasteropoda, brachiopods, and joints of small encrinal stems 
and plates ; the whole cemented by calcareous spar in a manner similar to 
many organic limestones. He observed, however, that the pores of the 
crinoidal remains were injected by a peculiar mineral, readily distinguishable 
in thin transparent sections, or on surfaces which had been exposed to the 
action of an acid, which dissolves the carbonate of lime and places in relief 
the injecting mineral. The minute structure thus revealed is precisely 
similar to that of recent crinoids studied by Carpenter, and will soon be 
described and figured by Dawson. Decalcified specimens exhibit a congeries 
of curved, branching, and anastomosing cylindrical rods of the replacing 
mineral, sometimes forming a complex network, which under the microscope 
resemble the coralloidal forms of aragonite known as Jlos ferri, and present a 
frosted crystalline surface. The same mineral, as observed by Dr. Dawson, 
occasionally occupies larger interstices among the fragments, and was evi- 
dently deposited before the calcareous spar which cements the whole mass. 
When this limestone is dissolved in dilute hydrochloric acid, the residue, 
washed by decantation, equals from five to six per cent, of the weight of the 
mass, and is seen under a microscope to consist entirely of the casts composed 
of the mineral just noticed, mixed with about one-fourth of coarse silicious 
sand. This matter is pale greyish-green in colour, but when calcined becomes 
of a bright reddish-brown, without change of form. 
The Boulder Drift and Esher Hills of Ireland. — Sir Richard Griffith, F.R.S., 
described these to the British Association (Edinburgh), and also the position 
and composition of the erratic blocks of that country — a subject to which 
he has paid much attention for the last sixty years. By the aid of a map, 
he described the rocks, and showed that the boulder drift was older than any 
