A phrase or two from the text can make all the difference when searching for a song; titles are often misunderstood or mis-spelled, as is the case with this one, which is properly called Cairn O' Mount. Armed with the bit you quote, it was easy to find; evidently it is a poem written by Alexander Balfour (1767-1829). It can be seen at Brechin: The Ancient City: Cairn O' Mount.
The site compilers describe it as "From A North Country Garland"; there have been several publications of this title, but I take the book in question to be James Maidment's A North Countrie Garland (1824). Can you provide any information about the tune you've heard it sung to?
CAIRN O' MOUNT
(Words by Alexander Balfour, 1767 - 1829)
As I rode down by the Brig o' Dye
And past yon hill o' broom,
A maiden sang right merrily,
Just as the sun gaed down.
"It's Cairn o' Mount is bleak and bare,
And cauld is Clochnaben'
And you will see the snow lie there
Alang the summer's end."
I lighted off my dapple grey
And walked by her side,
Saying, "Lassie, I have lost my way
Upon your moors so wide.
"Oh war me o' your face so fair,
Your een so bonnie blue,
The longest day I'd blythely share
To kiss your cherry mou'.
"Oh, lassie, will you gang wi' me,
And leave your cauldrich glen?
Wi' a' my kin ye'll bear the gree,
There's wealth baith but and ben."
"Wi' silks and satins buskit braw,
And ribbons for your hair,
And maids to answer when you ca',
So, can you wish for mair?"
"O lassie, ye maun think a wee,
My lands are far and wide,
I've gold in banks, and ships at sea,
So come and be my bride."
"My father left me lairdships twa,
A coach at my command,
I'll make you lady o'er them a',
If you'll give me your hand."
"Though Cairn o' Mount is bleak and bare,
You're no a match for me;
My Donald he is a' my care,
Ride on and let me be."
"He meets me on yon hill so green
His heart is leal and true
If Donald heard my angry scream
He soon would make you rue."
"O, lassie, think, your Donald's poor,
Has neither horse nor coo;
A shepherd straggling o'er the moor
Is not a match for you."
"Cairn o' Mount is bleak and bare,
And cauld is Clochnaben;
I'd rather meet my Donald here
Than be fair Scotland's queen."
"O lassie, I am loathe to tell,
You throw your love awa;
Your Donald brawly kens himsel'
Last gloamin' what I saw."
"As I rode by his shielin' door
I spied a Highland maid,
Your Donald kissed her o'er and o'er,
And rolled her in his plaid."
"Though you would swear wi' solemn oath
What you have told to me,
I would not dread my Donald's faith
But say, 'Base loon, ye lee."
It's he's thrown off his lowland dress,
Combed down his yellow hair,
Saying, "Lassie ye've been true to me,
And now we'll part nae mair."
"Nae mair I'm shepherd o' the glen,
But laird ayont the Dee;
And since ye have been true to me,
I'll aye prove true to thee."
Presumably from James Maidment's A North Countrie Garland (1824). I don't know whether there's a long-standing tune associated with it, or whether it has been recently set.