XXX ' PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



About the year 1833 lie was first smitten with a love of geology, 

 on meeting at Barmouth with Prof. Sedgwick, and making, hammer 

 in hand, mountain excursions with that most captivating of geologi- 

 cal companions in parts of IS'orth Wales. The study soon deeply 

 interested the mind of Mr. Hopkins, and he extended his excur- 

 sions in successive years to Scotland, Derbyshire, the Lakes, and 

 the north of France. His chief desire was to place the physical 

 portion of the science on a firmer basis, to free it from unverified 

 views, and to support its theories upon clear mathematical de- 

 monstrations. 



With this object in view he commenced a series of discussions, 

 the results of which have been pubHshed in a long list of papers in 

 the * Cambridge Philosophical Transactions,' in those of the Eoyal 

 Society, in the ^ Eeports of the British Association,' and in our own 

 Quarterly Journal. 



One of the earliest and most celebrated of Mr. Hopkins's mathe- 

 matical inquiries connected with geology was on the effects which 

 an elevatory force acting from below would produce upon a portion 

 of the earth's crust. Certain definite directions of upward -acting 

 force being assumed, the nature of the tension upon the up -raised 

 but still unbroken strata was determined, and it was shown what 

 would be the direction of the resulting fissures, afterwards known 

 to us under the various aspects of faults, lodes, and trap-dykes. After 

 deahng with the simple case of a single fissure, he , advanced to the 

 consideration of a system of parallel fissures, which he concluded 

 could not have been formed consecutively. Hence, although not re- 

 quiring that the total elevation should have taken place at once, he 

 stated that the whole of any disturbed district, characterized by a con- 

 tinuous system of parallel dislocations, must have been elevated simul- 

 taneously. After this, whatever tendency there might be to form a 

 second system of fissures, it would be in a direction perpendicular to 

 that already existing. 



About 1837 Mr. Hopkins applied himself to the very difficult al- 

 though promising investigation of the varying effects of the sun's 

 and moon's attraction (especially precession and nutation) according 

 as the earth be supposed to be solid or to be formed of a fluid inte- 

 rior surrounded by a rigid shell. It was a fascinating attempt to ob- 

 tain from astronomical facts that evidence respecting the deep interior 

 of the earth which is denied to the test of our senses. He found 

 that the precession and the lunar nutation would be the same in both 

 cases, or that the difference would be inappreciable to observation, 

 - — and that the solar nutation would remain the same, unless the 

 thickness of shell had a certain value, something less than a quarter 

 the earth's radius, in which case the nutation might become much 

 greater than for the solid spheroid. In addition to these motions, 

 the pole of the earth would have a small circular motion depending 

 entirely on the internal fluidity, but which would for any, except the 

 most inconsiderable thickness of the shell,be practicably inappreciable. 

 These views were brought before the Eoyal Society in 1839 and 

 1840, and in 1847 were presented in a different form with additional 



