76 REPORT— 1846. 
shade and moisture, numerous ferns, and even tree ferns are found, as in Silhet. 
The strata of the Burdwan coal-basins of Ranigunge and Chinakooree yielded the 
author abundant remains of the Ranigunge reed, Vertebraria indica, the marsileaceous 
genus, Trizygia speciosa, and species of Pecopteris, Glossopteris, &e. G. Browniana 
is interesting as having been found in these ceal-fields, and according to Brongniart, 
in New Holland, in the coal of the Hawkesbury river, near Port Jackson. Zamia 
Buchanani has also been found, and a palm which has been called Zeugophyllites 
calamoites. With a little more moisture, or even the umbrageous covering of a 
forest, these, and other similar plants, would grow with luxuriance in these localities. 
Seeing therefore that heat, with moisture, is capable at the present day of sup- 
porting a vegetation similar to that of coal-fields, it would in ancient times only have 
required the presence of heat and moisture for the vegetation of coal-fields to have 
flourished. If the mass of the earth was in ancient times of a higher temperature, 
as is inferred from many geological and zoological phenomena, it is evident that, 
water being present, copious evaporation would necessarily take place as it now does 
in tropical countries. ‘ If the internal heat were uniform at different points of the 
globe’s surface, then would the evaporation be uniform, and there would be an 
absence of those upper and lower currents of the atmosphere which now carry the 
heated and moisture-loaded air of the tropics to polar regions, and send the cold air 
of the latter towards the equator. As.the air, loaded with moisture, ascended into 
the atmosphere, it would at length reach an elevation where the reduction of tem- 
perature would proceed beyond the point of deposition of moisture, and the whole 
of what had been raised by the aid of heat and air would be constantly depositing in 
the form of clouds and rain. Moisture would thus everywhere be preserved, and 
the cloudiness from the steady action of the heat below and of the cold above would 
necessarily also be constant. This would produce uniformity of temperature; for 
radiation from tle surface would be obviated, and the solar rays would not penetrate 
the cloudy canopy more than they do in rainy weather at the present time. In 
such a climate, tropical plants would be able to grow equally well in any latitude, . 
and there might be intermixed with them many others to which dryness was not 
essential. In conclusion, the author remarked, such a cloudy canopy may be observed 
to a partial extent, even in the present day. Humboldt has described it as occurring 
on the Andes ; the author had himself observed it for days together on the Hima- 
layas, and partially so during the whole of the rains; Dr. M‘Clelland and others 
have described it as occurring for months together in the valley of Assam. If it ex- 
isted in northern regions in early times, and the sources of heat were, as Dr. Royle 
assumed, internal, then could tropical vegetation not only exist in polar regions 
during the summer season, but it would not be destroyed in winter. Growth would 
only be stopped, as in the present day, during the darkness of night. As the 
internal heat diminished and receded from the surface, the cloudy canopy would by 
degrees be at a lower and a lower elevation, until, like the snow-line of the present, it 
would be at the surface of the earth in high latitudes. These regions would become 
as they are now, and immediately under the influence of external cold, and thus 
a glacial might succeed a tropical vegetation. In situations where a lofty peak 
raised itself above the canopy of clouds, it would become exposed to the cooling 
effects of radiation, and would, as in the present day, attract to itself and condense 
much of the floating moisture of the atmosphere, and give origin to mighty and rapid 
rivers, which would plough the mountain side and overspread the level plain. 
A Synopsis of the Classification of the Genera of British Birds. 
By Joun Hoce, MA. F.RS., PLS, Sc. 
The author, having completed his classification of birds,which has been carried out 
on the same principles as that portion published in the Report of the Fourteenth 
Meeting of the British Association, although in some respects modified from it, gave 
in this communication his arrangement of the genera of the birds hitherto met with 
in the British Islands. 
It will be seen that he has been compelled to increase the families, and that he 
has not inserted the subfamilies, esteeming them unnecessary, and as too much 
lengthening the classification. The author has been very careful in the choice of the 
eres Al eee 
