40 REPORT—1843. 
Irish House of Commons, he retired from the bar. For his first efforts, a series of 
essays, he received the Copley medal, and he was elected a Member of the Royal 
Trish Academy. Chemistry and mineralogy were the sciences to which Mr. Kirwan 
particularly applied herself. He was fond of metaphysics, and wrote a volume on 
logic. He also bestowed much attention on meteorology, and his essay on the vari- 
ations of the barometer has obtained the approbation of Dalton and others. 
GEOLOGY AND PHYSICAL GEOGRAPHY. 
On the Distribution of Erratic Blocks in Ireland, and particularly those of the 
North Coasts of the Counties of Sligo and Mayo. By Ricnarp Grirritu, 
F.G.S. 
Ir we look to the distribution of erratic blocks as indicative of the direction of the 
currents by which they were distributed, we find in Ireland generally that they were 
carried from north-west to south-east, though the current was often modified by the 
opposition of mountain ridges. 
The prevailing component of our drift is rolled limestone and clayey matter, de- 
rived from our great limestone field, which occupies two-thirds of the island. This 
matter is seldom stratified: it consists of an heterogeneous mass of large and small 
rounded pebbles of limestone, intermixed with clay, fine gravel, and rarely siliceous 
sand. 
This mass often exceeds 100 feet in thickness; it pervades all our valleys, and 
even the interior of some of our mountain ranges, to a considerable height ; it occurs 
either in one thick mass, resting on the rock, or in the form of those remarkable low, 
but steep gravel hills called Eskers. The prevailing direction of our mountain ridges 
is from north-east to south-west at right angles to the supposed direction of the 
current, and, as might be expected, we find the gravel-banks and detritus distributed 
on the north-western declivities of the hills, and intruding into the interior valleys ; 
the slate districts of Armagh, Cavan, Monaghan, &c. might be instanced. 
In some instances, in the granite and slate districts of Wicklow, as in the valley of 
the Slaney, the limestone gravel has passed through the valleys of the mountain ridge, 
and has formed a deposit of limestone pebbles, eastward to the range of Mount 
Leinster, and spread over the slate country in the neighbourhood of Newtownbarry in 
Wexford. 
Similar facts may be observed in the Slievebloom mountains, as well as the Galtees 
and Monavoullagh mountains of the counties of Limerick and Waterford. 
Limestone gravel is found on the western declivities in the valleys of all the moun- 
tain ranges mentioned, but none has been observed on the eastern declivities. We 
may hence infer, that where the mountains were of sufficient height, the currents 
‘were interrupted, and the gravel did not pass to the eastward. The summit of the 
Baltinglass hill in the county of Wicklow is elevated 1256 feet above the level of the 
sea. Its southern and western declivities are covered by limestone gravel to an ele- 
vation of upwards of 800 feet, but none occurs on its eastern declivity. The neigh- 
bouring hills of Spinan’s and Brusselstown are also covered by limestone gravel to 
the height of 880 feet ; hence we may assume that the transporting force did not ex- 
ceed an elevation of 1000 feet. 
On the top of the gravel deposit, and independent of it in many localities, are 
found boulders of granite, and red and light gray conglomerate, scattered over the 
surface of the country, but rarely, if ever included or intermixed with the gravel lying 
below. Owing to a peculiarity in the composition of granite of certain districts, it 
is not difficult to detect the locality from which each was derived; hence he had no 
hesitation in saying that he found small boulders of the granite of Cunnemara in 
Galway to the east of the Slievebloom mountains, in the line of the valley of Roscrea. 
Similar boulders, but larger, occur in the King’s County, and also in the limestone 
district of Galway, indicating that the direction of the line of transport was from 
north-west to south-east through a very large portion of Ireland; this, however, is 
not universal. t 
