xxviii REPORT— 1858. 
with a panic.. The specimen he collected was examined by my successor 
at the Royal College of Surgeons, Prof. Quekett; and that experienced 
microscopist could detect only inorganic particles, such as fine quartz sand, 
without any trace of Diatomacez or other organic matter. Dr. | awson has 
obtained a similar result from the examination of the material of a shower 
of moist dust or mud which fell at Corfu in March 1857: it consisted for 
the most part of minute angular particles of a quartzose sand. 
Here, therefore, is a field of observation for the microscopist, which has 
doubtless most interesting results as the reward of persevering research. 
Many ‘ dust-showers ’ consist in greater or less proportions of microscopic 
organisms, but not all. To determine the source of these organisms is the 
legitimate aim of such researches. It must be remembered, also, that the 
expression ‘spontaneously developed’ in the atmosphere, may only mean 
what is meant when it was formerly applied to the internal parasites of man 
and animals, viz. ignorance of the true mode of origin. And since per- 
severing observation and experiment, in regard to tape-worms and ascarides, 
have thrown such new and unexpected light upon their origin and migrations, 
so the like result may reward similar labours applied to the parasitic ‘ dust- 
showers ’ of the atmosphere. 
Microgeology.—The microscopic organisms hitherto observed in the oldest 
fossiliferous deposits, Silurian Greensands, for instance, are spicula of 
Spongie, siliceous Polycystinee, and calcareous Foraminifera. 
Ehrenberg has discovered that the substance of the greensands in stratified 
deposits, from the Silurian to the Tertiary periods inclusive, is composed of 
the casts of the interior of the microscopic shells of Polycystinee and Fora- 
minifera. The soundings which have been brought up from various parts 
of the Atlantic and the Gulf of Mexico, consist chiefly of similar microscopic 
polythalamous shells, mingled with a greensand composed of easts of Fora- 
minifera. ‘Thus the mode in which a deposit was made at the bottom of the 
deep primeval ocean of the Silurian period, is illustrated by that which the 
microscope has demonstrated to take place under similar conditions at the 
present day. 
The earliest indubitable evidence of diatoms has been obtained from the 
Eocene strata; and the forms here determined have been for the most part 
identified with existing species. Exotic species are not distinguishable from 
the British; difference of climate seems not to affect or relate to specific 
difference, and the same exemption from such influence through the minute 
size and simple structure of the Diatomacez, seems to have been the chief 
condition of their geological longevity as species. 
To specify or analyse the labours of the individuals who of late years have 
contributed to advance zoology by the comprehensive combination of the 
various kinds of research now felt to be essential to its right progress, would 
demand a proportion of the present discourse far beyond its proper and 
allotted limits. 
