BURR AND BURKE : FOSSILS IN ROXBURY CONGLOMERATE. 181 
upon several species of the genus Artisia , particularly upon Artisia 
dista?is , figured by Grand ’Eury in Flore Carbon if er^ de la Loire. 
It is quite possible that the specimens figured are related to that 
form. It cannot, however, be denied that such vague markings 
have little determinative value and may even be of mechanical 
origin. 
While the writers are disposed to believe that these forms cannot 
be identified with certainty, they nevertheless feel confident that 
they are true fossils. The several geologists who have passed judg¬ 
ment upon them, have, with one exception, expressed themselves as 
satisfied of their organic origin. The other view is that they are 
due to mechanical action, — that they are akin to stylolites. It 
is difficult to see upon what this opinion is based. The speci¬ 
mens figured certainly bear little resemblance to the ordinary forms 
of stylolites. As generally defined, stylolites are forms produced in 
rocks by displacement or the development of slickensides about a 
portion protected by a shell or other hard capping. Such forms 
have characteristically slickensided surfaces, usually with strongly 
marked longitudinal striations, and frequently with the development 
of secondary minerals. The forms under consideration show no 
trace of longitudinal striations. The surfaces are not smooth after 
the manner of rubbed surfaces. There is, so far as can be seen, no 
development of new minerals. In short, the phenomena of slicken- 
siding are altogether absent. Stylolites are of small size, seldom 
exceeding four inches in length or two in diameter. The specimens 
figured average about four inches in diameter, and the largest is over 
a foot in length, with the total length not known. There is no 
reason why stylolites should have a circular cross-section. It would 
be strange indeed if, as in this case, all the specimens found in a 
limited area should have this form. There seems then to be no 
reason whatever for thinking that the surfaces of these specimens 
were developed by differential movement. It should be added that 
stylolites usually occur in limestones or in fine-grained shales, and 
have never, so far as is known, been reported from coarse sandstones. 
It may be suggested that these forms are concretionary. Cylin¬ 
drical or rod-like concretions are not unknown, and, so far as the 
form is concerned, these specimens might be of such nature. If 
the forms are concretionary, the material of which they are made 
up should differ, in a determinable way, from the material of the 
matrix. This does not appear to be the case. In both cast and 
