On the Phenomena of Sleep. 137 
Zavas ;-but that part which entered the sea is seen, at the time of 
low-water, to be divided into the prismatic form which charac- 
terizes basalies. 
fee Has 
T hope, Sirs, that Mr. Smrruson will read with interest in your 
Journal the statement of various geological facts which he had not 
had the opportunity of observing, himself. He will thus under- 
stand, surely, that geology is tco extensive a science for a general 
system being formed with any certainty, witheut having ebserved 
the different characters of the surface of the ear th, not in one 
country only, but in many; as in some countries the same pha- 
nomena are attended with others which may prevent mistakes. 
And with respect to information received from countries unknown 
to ourselves, he will also conceive that no reliance is to be placed 
on the observations of those whose accounts manifest that they 
have considered the phenomena with a mind prejudiced by some 
previous hypothesis to which they are higoted. 
I have the honour to be, sirs, 
Your most obedient servant, 
To Messrs. Nicholson and 7 ‘loch. Jai. ‘Da Lucy 
XXVIII. Onthe Phenomena of Sleep. By a Correspondent. 
‘| HE célebrated physiologist Dr. Whytt suggested that conges-~ 
tion of blood in the head was the immediate cause of sleep. 
Though this position was supported by a large induction of facts, 
it soon fel] into disrepute, upon the discovery of congestion under 
circumstances no way analogous, as in lunacy, convulsions, insa- 
nity, and intoxication. Dr. Whyit’s views however have latel 
‘been revived, and extended with some modifications to an ample 
explanation of all the phenomena. It is. now ascertained that 
there is a congestion of blood in the head during sleep; but that 
congestion alone is insufficient, a retarded circulation being also 
necessary, For this modification we are indebted to Dr. Park, 
the author of ‘ An Inquiry into the Laws of Animal Life.” From 
this work, which is a general cutline of physiological science, the 
grounds upon which the phenomena of sleep may be explained 
are chiefly extracted. This writer reasous entirely on an indue- 
tive or analytical process: that which I shall use will be syn- 
thetic, applyi ing his principles to a very minute statement of facts, 
and occasionally advancing ideas of my own. 
Two important facts are established in this work; one relating 
to the connexion between the function of every organ and its cir- 
culation, and the other to the changes incidental to the cireula- 
tion itself. ‘The former shows that the faculty of feeling and the 
power 
i 
