80 
THE GEOLOGIST. 
rocks far below the surface, which have never appeared ; and that the 
gradual disappearance of the anthracitic tendency has been simply the 
dimiuishing distance from the heat which has caused the change. The 
question may be asked, Why are only the " North Crop coals " anthra- 
citic, while the " Upper Measure coals," which are worked only a few 
miles distant, are bituminous 1 For instance, at Trimsacau, near 
Kidwelly, the coals are stone-coals, while at Llanelly, only six miles 
distant, the coals (upper measure) are bituminous. I consider the 
reason to be that the changes were subsequent to the deposition of 
the lower measures and prior to the upper ones ; for we must not 
forget the vast geologic times that passed between the formation of 
the upper and the lower measures, during the deposition of the 
immense thickness of Pennant rock. According to this notion, the 
anthracitic change was all completed before the deposition of the 
upper measures. If the change were going on now, I cannot under- 
stand how the upper measures, which are so near the seat of change, 
can escape the same effects. In addition to what I have stated, I may 
add that in all the accounts of anthracitic coal-fields which I have 
looked through, whether belonging to the old coal-period or to the 
secondary eras, I have observed that disturbances and the presence 
of igneous rocks are described as existing in the great majority. 
FOREIGN CORRESPONDENCE. 
By Dr. T. L. Phipson op Paris. 
Shifting Sand-hills of the Mediterranmn — Sand-hills or Dunes on the 
Coast of Flanders — Encroachment of the Sea — Vegetation of the Dunes 
— Suhtei-raneous Noises — Crystalline forms of Anglesite — Analysis of a 
Meteorite — Minerals in Aerolites — Meteoric Stones and their relations 
to Geology — The Volcano in the Island of Bourbon — Temperature of 
the Earth's crust at inconsiderahle depths — Activity of Mount Vesuvius 
— Earthquakes in Turkey — Submarine Volcano near Legliorn — 
Erratum : Iron-alum. 
The learned Geologist of Montpelier, M. Marcel de Serres, has just 
communicated to the Paris Academy of Sciences the following facts 
concerning the dunes, or shifting sand-hills, of the French Medi- 
terranean coasts. These sands are first thrown upon the shore by 
the sea ; when dry, they are carried inward by the winds, to the 
