DEPOSITS OF SCOTLAND. 379 
of the Lower Old Red Sandstone appear,—curious, as the 
most ancient ganoids known to the geologist, and further, from 
the circumstance that, while the still older placoids of the Up- 
per Silurian system exist merely as detached teeth, spines, and 
shagreen points, these Old Red fishes exhibit in the better 
specimens the entire outline of the original animals, with not a 
few of their anatomical peculiarities. It is from this formation 
that our knowledge of the oldest skulls, of the oldest vertebral 
columns, and of the oldest pelvic and thoracic arches, anywhere 
preserved, is to be derived. With the fish we sometimes find 
associated, though not often, specimens illustrative of what 
seems to be our most ancient terrestrial F lora,— club-mosses, 
— reed-like casts and impressions, streaked longitudinally, like 
the interior of the calamite, but apparently without joints,— 
what appear to be ferns,— and, in at least one unique specimen, | 
a true wood of the araucarian family,—the oldest which has 
yet presented its structure to the microscope. In some locali- 
ties, such as Cromarty, Thurso, and perhaps Moray, the 
various ichthyic species of the formation seem to have been 
pretty nearly ascertained and collected: for several years I 
have not succeeded in discovering from the several Cromarty 
deposits a single new species; and my friend Mr. Dick, though 
permanently resident on the spot, has had a similar experience 
at Thurso. Species of the rarer kinds may, however, long 
elude very assiduous search, and yet turn up at last; and in 
the course of the present twelvemonth I have received from a 
tract of shore near Cromarty, which I have walked over many 
hundred times, an ichthyic species,— the Diplacanthus crassis- 
pinus,— of which my collection had possessed no previous 
specimen. I owe it to the kindness of Miss Catherine Allar- 
dyce,— a lady who, to a minute knowledge of not a few other 
branches of natural science, adds an intimate acquaintance 
_with the fossils of our northern formations, and whose skill in 
