472 Reports and Proceedings — 



connected with it are more distinctly visible on the under than on 

 the outer surface of the test, and the canalets connected with the 

 lobe spread over the anterior slopes of the shield and extend to the 

 anterior margin. In the tuberculated species they connect by hollow 

 spines with the outer surface. In one species they cover a wider 

 space than in the others, extending some distance behind the ocular 

 ridges and over the front of the glabella. 



3, Decoration of the Test. — In all the Acadian species of this group 

 but one, the surface of the test at maturity is covered with tubercles 

 and spines similar to the surface-markings of Conocoryphe Sulgeri, etc. 

 In the earliest stages, however, no such tubercles are found, but 

 the surface appears smooth or scabrous. In CtenocepJialus Matthewi 

 the surface, in the first three stages of growth, appears smooth ; in 

 the fourth, tubercles begin to appear, and about the fifth stage all 

 projecting parts of the test are studded with them. Those on the 

 glabella and frontal lobe are arranged in transverse rows ; those on 

 the cheeks in interrupted rows conforming more or less to the 

 periphery of these protuberances. Towards the adult stage these 

 tubercles and spines become more irregular in position and number, 

 conforming in this respect to the law of development in the Ammonites, 

 expounded by Professor Alpheus Hyatt. 



7. On rLUXION-STRUCTURE IN TiLL. 



By Hugh Miller, A.R.S.M., F.G-.S., Geological Survey of England and "Wales. . 



IT has long been recognized as one of the characteristics of the 

 Till that its long-shaped boulders are striated lengthwise. They 

 have, as it has been concisely expressed, been " launched forward 

 end-on." From the minute and magnifiable striee upon the smaller 

 {e.g. almond-sized) boulders it also appears that these at least have 

 been carried forward, involved in the matrix, and were glaciated 

 chiefly by its particles. Under the microscope these particles exhibit 

 most of the varieties of form and glaciation that are found among 

 larger boulders. The structure of the Till in open situations shows 

 that the axes of its stones have been turned by a common force in 

 the direction of glaciation ; it exhibits a rough structure comparable 

 to the fluxion -structure of igneous rocks, the smaller boulders 

 dividing around and apparently drifting past the larger, like the 

 tide round an anchored skiff. These structures, which have been 

 found by the author over many hundreds of square miles, chiefly in 

 the North of England, indicate that at least a surface-layer of the 

 Till was dragged along, with a shearing movement of particle upon 

 particle, producing intimate glaciation within its mass. Proofs are 

 adduced that this moving layer was in general a surface-layer only, 

 and that the Till did not, as has often been supposed, move forward 

 en masse, licking up its additions from beneath. This is the only 

 intelligible explanation of the order (as well as the structure) of the 

 Boulder-clays of which the author has any practical knowledge. 

 In up-lying situations, where the drift consists of raw material, 

 fluxion-structures are seldom detected. In sheltered spots they are 

 not generally developed. They are characteristic of well-kneaded 



