24° A. C. G. Cameron—Hertfordshire Subsidences. 
In Britain, the genus Girvanella has, so far, only been recognized 
as occurring in the Ordovician limestones of Ayrshire. I have, 
however, found some of the Carboniferous limestones of the North 
of England to contain largely an ill-preserved organism which will, 
I think, prove to be referable to Girvanella. As previously pointed 
out, the genus occurs in the Ordovician rocks of North America. 
This is shown by the fact that certain of the specimens from the 
Cincinnati Group of Indiana sent to me by Mr. E. O. Ulrich as 
belonging to the Stromatocerium richmondense of Mr. 8. A. Miller, 
prove on examination to belong toa species of Girvanella, specifically 
distinct, | think, from our British species, as shown by the greater 
minuteness of “its tubes. I see, also, no reason to doubt that the 
fossils from the Chazy Limestone of North America, for which Prof. 
Henry M. Seeley has proposed (Amer. Journ. Sci. and Arts, 1885, 
vol. xxx. p. 395, 1885) the new generic name of Strephochetus, are 
in reality referable to the genus Girvanella. It is probable that the 
Chazy form (Strephochetus ocellatus, Seeley) is specifically distinct 
from Girvanella problematica, but its generic identity appears to be 
indubitable.'. Prof. Seeley seems disposed to think that the curious 
fossil described by Prof. James Hall, from the Calciferous Limestone, 
under the name of Cryptozoén proliferum (Thirty-sixth Ann. Rep. of 
the State Cabinet, pl. vi. 1884), may be related to Girvanella ; but I 
~ cannot think that such a relationship—supposing it to exist—can be 
one of generic affinity. The fossil for which Prof. Hall has proposed 
this name is not only comparatively gigantic in point of size, but its 
internal structure, so far as may be judged from the incomplete 
provisional diagnosis given by its author, is altogether different, 
since it is stated to consist of branching and anastomosing canaliculi. 
Lastly, with regard to Prof. H. M. Seeley’s reference of Girvanella 
(=Strephochetus) to the calcareous sponges, it need only be said that 
the structure of the genus, so far as recognized, shows nothing 
which would warrant such a reference, and that it would be essential 
to the establishment of this view, according to our modern lghts, 
that the organism should be proved to possess definite spicules. 
ITV.—HeERTFORDSHIRE SUBSIDENCES. 
By A. C. G. Cameron. 
UBSIDENCES are by no means unusual amongst the arable 
lands in the Chalk districts of this county. No one, who has 
travelled in these parts, can have failed to notice the numerous holes 
and dells dotted about the fields in all directions, many of which 
have fallen in, or will do'so, in course of time. Nearly all of them 
mark spots where the Chalk has been dug up for chalking the land, 
which is then said to work better.” 
On the crown of some hill or ridge, it is no uncommon sight to 
1 Dr. Hinde has already pointed out that Strephochetus, H. M. Seeley, is identical 
with the previously described Girvanella, and has further shown that the Siphonema 
of Dr. Bornemann, supposed by its describer to be a calcareous Alga, is likewise a 
synonym of Girvanelia (Grout. Maa. 1887, Dec. III. Vol. IV. p. 227). 
2 Gravel soils, such as fringe the modern alluvium of rivers and streams, are 
chalked as well as the stronger soils. 
