414 
the upper and lower surfaces are covered so abundantly with 
scales of mica, that it may frequently be scraped off with the 
fingers. 
The foot-prints and worm-tracks occur on both sides of 
the slabs, the indentations being always on the upper surface, 
and the reliefs on the lower. 
Upon one slab, I have, without much difficulty, decyphered 
nearly forty continuous impressions of the same track. The 
stride appears to be somewhat more than an inch, and behind 
the marks are frequently short furrows, similar to those 
already described, where the feet have been drawn along the 
surface. No marl or clay is found in connection with the 
stratum, the preserving agent in this instance being the in- 
terposed micaceous scales. 
Stone from the neighbourhood, and out of another part of 
the same quarry, is well known in Sheffield, being used as 
common roofing slate. 
At Walkley, about IJ miles from Sheffield, I found, in 
September last, (1841^, a stratum formed of exceedingly fine 
laminae, containing similar foot-prints (No. 5). The mineral 
composition is the same as the last mentioned ; scales of mica 
being interposed between the layers, which are so thin that 
the same impressions appears on both sides, on the upper as 
indentations, and on the lower as reliefs. 
Many singular impressions, besides foot-prints, will be ob- 
served on this stone; these I attribute to the dropping of 
water upon the sand, and so numerous are they over the 
entire surface, that if I had not become somewhat familiar 
with the little reptile, whose footsteps I had previously so 
often followed, I should have doubted if I had detected him 
at all in this instance. 
It is difficult to come to a satisfactory conclusion as to 
some of the marks ; the progression of the deposit must, 
evidently, have been exceedingly slow ; and yet the im- 
