132 Mr. Thomas Thomson on a [Feb. 



varies very much in different places. In some parts of the 

 immediate neighbourhood of this city, we find low hills of a 

 thick miry clay, full of water- worn stones, and quite des- 

 titute of fossils. In others, and particularly under Glasgow 

 itself, there occurs a deposit of very pure sand, of consider- 

 able thickness, rising in one or two places to a considerable 

 elevation. This arenaceous deposit would appear to extend 

 to a considerable distance, since the red conglomerate in the 

 neighbourhood of Helensburgh, at the distance of twenty- 

 six miles from Glasgow, is also covered with a very line 

 sand to the depth of eight or ten feet, in which shells are 

 said to have been found during the digging of the founda- 

 tions of Roseneath Castle. Here, however, there is also 

 interposed between the sand and the secondary rocks, a bed 

 of stiff clay very similar to the clay about Glasgow, by the 

 position of which we may perhaps conclude, from analogy, 

 that the corresponding clay at Glasgow is below the sand, 

 and though no distinct section has there been obtained, yet 

 the more frequent occurrence of the arenaceous beds might 

 perhaps lead us to the same conclusion. 



In the neighbourhood of Dalmuir, about 8 J miles from 

 Glasgow, a section of the sand deposit is exposed by a small 

 stream known by the name of Dalmuir burn. A few years 

 ago, the proprietor of that part of the country found it con- 

 venient to alter the course of this stream. During the 

 formation of the new course a great deal of sand was cut 

 away, and in one particular place the workmen were sur- 

 prized to find that they were digging through a mass of 

 shells. The extent of the spot in which the shells are 

 found is so limited that it would probably have remained 

 unknown had not the overseer of Mr. Dunn's estate been 

 kind enough to point it out to me when I was in that 

 neighbourhood collecting fossils from the shale beds con- 

 nected with the coal. 



The locality in which the fossils are exposed is situated on 

 the banks of the Dalmuir burn, about 100 yards above the 

 bridge by which the road from Glasgow to Dumbarton crosses 

 it, and about a mile from the Clyde. The current of the 

 stream is not very rapid, so that the bed of shells is probably 

 not more than 20 feet above the level of the Clyde, which at 

 that place is sensibly salt at high water. The breadth of 



